Does Every Animal Dream? | What Science Can Show

Not proven—many mammals and birds show dream-like sleep, while many other animals have sleep without clear signs tied to dreaming.

When people say “dream,” they usually mean an inner stream of images and feelings during sleep. In humans, you can wake someone up and ask what was going through their mind. That single step makes dreaming easy to confirm.

With animals, that step is missing. So researchers use a practical stand-in: sleep states that, in humans, often line up with dream reports. You’ll see phrases like “REM-like” or “active sleep” for this reason.

Below is a plain-language guide to what can be measured, what those signals mean, and where the evidence is strong versus thin.

What Scientists Mean By Dreaming

Two ideas get mixed together in everyday talk:

• Dreaming as inner experience: the private “movie” in the mind.
• Dream-like sleep: a sleep state with features that, in humans, often come with dreams.

The second idea is what scientists can test in animals. In people, vivid dream reports tend to follow awakenings from REM sleep, which is marked by rapid eye movements, active brain signals, and reduced muscle tone. The National Institute of Neurological Disorders and Stroke summarizes these REM features and the link to dreaming in its public sleep guide. NINDS sleep basics is a clear baseline for what “REM” means in humans.

Once you have that baseline, the animal question becomes narrower: does the species show a sleep state that resembles REM in measurable ways?

Do All Animals Dream During Sleep? How Researchers Judge Evidence

Because animals can’t describe their dreams, researchers rely on three tiers of evidence.

Tier 1: Reports After Awakenings

This is the gold standard and it is human-only in routine lab work.

Tier 2: REM-Like Sleep Signatures

If a species shows stage cycling plus REM-like markers (eye movements, active brain patterns, muscle tone shifts), it has a strong case for dream-like sleep. That still doesn’t confirm dream content.

Tier 3: Sleep Behavior Without Fine Brain Measures

In many species, scientists can show sleep using behavior: a regular rest state, lower responsiveness, and rebound sleep after deprivation. That backs “sleep,” not “dream.”

What We Know Across The Animal Kingdom

Mammals are the clearest group. Many species show REM and non-REM stages that resemble human sleep architecture. If you’ve seen a dog twitch or a cat paddle its paws, that often happens during REM in lab recordings, though twitching alone is not proof of dreaming.

Birds also show REM and non-REM sleep. Their REM episodes are often short, yet the pattern is still recognizable in recordings.

Reptiles show sleep states with different brain rhythms in some lab studies, and REM-like activity has been reported in select species. The strength of evidence varies a lot by species and by measurement setup.

Fish show sleep-like rest and rebound sleep, and some studies report brain-state switching that invites comparison with vertebrate sleep stages. Across fish lineages, results are mixed.

Invertebrates add more uncertainty. Fruit flies show sleep-like behavior and brain activity changes during rest. Bees show rest phases with reduced movement and altered responsiveness. These systems are great for controlled experiments, yet the bridge from sleep to dream experience is still wide.

Cephalopods sit in the spotlight because they show complex behavior while awake and have distinct sleep states. A 2023 paper reports an “active sleep” stage in octopuses with wake-like skin patterning and neural activity that resembles vertebrate REM features. Octopus active sleep study (PMC) shows the measurements and why researchers describe this as REM-like.

Arachnids entered the conversation after work on jumping spiders documented repeated bouts of retinal movements during sleep-like rest, along with limb twitches. Jumping spider REM-like state (PMC) is often cited because the retinal movements can be seen directly in juveniles.

What Counts As A Dream-Like Signal

When you strip away the hype, most “animals dream” claims rest on a short list of measurable cues:

• Stage cycling: a repeating switch between quiet sleep and an active sleep state.
• Eye or retinal movement bouts: clustered movements during active sleep.
• Muscle tone shifts: a relaxed body paired with an active brain state, sometimes with small twitches.
• Sleep rebound: extra sleep after forced wakefulness, showing a regulated need for sleep.

These cues do not prove inner dream scenes. They do back a claim that the animal enters a sleep state that resembles the one where humans often report dreams.

Three Claims That Headlines Often Blend Together

It helps to separate three statements that are not the same:

1. This animal sleeps. Often testable with behavior and sleep rebound.
2. This animal has REM-like sleep. Testable in some species with brain and eye measures.
3. This animal has human-like dream experiences. Not directly testable in non-human species.

Many animals fit #1. Mammals and birds often fit #2. #3 remains unconfirmed for non-human species, even when REM-like sleep is clear.

Dreaming Evidence By Group And What Still Blocks Certainty

This overview is a map, not an exhaustive catalog. It shows where the evidence tends to land with today’s tools.

Animal Group	Signals Linked To Dream-Like Sleep	Big Unknowns
Mammals	Clear REM and non-REM stages; rapid eye movements; reduced muscle tone	Dream content and frequency can’t be verified without reports
Birds	REM and non-REM sleep; short REM bouts; brain activation during REM	How bird REM maps to dream experience is unresolved
Reptiles	Multiple sleep states in some species; REM-like activity reported in labs	Stage definitions differ; limited data across many lineages
Amphibians	Sleep-like rest and reduced responsiveness; limited staging data	Few high-resolution recordings across species
Fish	Sleep-like rest and rebound sleep; brain-state switching in select studies	REM-like markers are inconsistent across species
Cephalopods	Quiet and active sleep states; neural activity and skin-pattern shifts in active sleep	Whether active sleep includes dream imagery is unknown
Crustaceans	Sleep-like rest and responsiveness changes in lab species	Stage cycling is not well mapped across the group
Insects	Sleep-like behavior; rebound sleep; brain activity shifts during rest	REM-like staging is debated; inner experience is unclear
Arachnids	Retinal movement bouts and limb twitches during sleep-like rest in spiders	Mechanisms and function links are still open

Why Cute Twitching Videos Aren’t Enough

Movement during sleep is easy to film and easy to misread. A twitch can come from reflex loops or random motor noise. That’s why researchers prefer a full package of signals, not a single behavior.

In the jumping spider work, the headline-grabbing part is not just limb twitching; it’s the repeated bouts of retinal movement during sleep-like rest. In the octopus work, the argument comes from coordinated changes across neural activity, breathing, and visible skin patterning during an active sleep stage. Both lines of evidence are stronger than “it moved in its sleep.”

How Scientists Study Dream-Like Sleep Without Words

The best studies combine multiple tools so the interpretation doesn’t rest on one shaky marker.

Method	What It Can Show	Main Limits
EEG or brain electrodes	Brain rhythms tied to quiet sleep vs active sleep; stage cycling	Hard outside labs; not feasible for many species
Eye or retinal tracking	Movement bouts during active sleep; timing of REM-like phases	Only works when eyes can be tracked cleanly
Muscle tone monitoring	Reduced muscle tone during active sleep; twitch timing	Twitching is not unique to REM-like sleep
Behavioral sleep criteria	Recurring rest state, lower responsiveness, rebound sleep after deprivation	Confirms sleep, not inner dream experience
Learning tasks	Links between sleep and later performance on memory tasks	Shows function links, not dream content
Neural imaging (limited species)	Which brain regions activate during sleep states	Limited to a small set of animals and setups
Pharmacology	How sleep states shift when brain chemistry is altered	Drug effects can be broad, complicating interpretation

So, Does Every Animal Dream?

If you mean “every animal has an inner dream narrative like humans,” science can’t back that claim.

If you mean “every animal has REM sleep,” the answer is also no. REM-like sleep is clear in mammals and birds. Outside those groups, evidence ranges from promising to thin, and many animals have not been studied with the right tools yet.

If you mean “many animals sleep, and some have an active sleep phase that resembles REM,” that statement matches what researchers can defend today.

How To Read Dream Claims Without Getting Fooled

• Check what was measured. Brain recordings and eye tracking carry more weight than behavior alone.
• Look for stage cycling. A repeating alternation between quiet and active sleep is a strong clue.
• Watch the wording. “REM-like” is cautious; “it dreams like we do” is a leap.
• Match the claim to the animal. Evidence from a mouse does not transfer cleanly to a sea star.

Where Research Is Heading

Smaller sensors and better video tracking are making it easier to study sleep in more species without heavy lab constraints. Researchers are also getting better at linking sleep states to learning and behavior, which can clarify what sleep is doing even when dream content can’t be measured.

The most honest takeaway is simple: the animal kingdom contains a wide range of sleep styles. Dream-like sleep is common in mammals and present in birds, with growing evidence in some invertebrates. “Every animal dreams” is a bigger claim than the data can carry right now.