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Swing by a swamp or some throng of cattails in the evening and the swell of ribbits and buzzing insects might convince you that sleep is not as necessary for the marsh world. And when it comes to the American Bullfrog, you may be right. The grey-brown carnivore (it mostly subsists on bugs) found throughout the continental U.S. and as far East as Nova Scotia, Canada, and as far south as Mexico and Cuba, has such strange sleep patterns that they seem to defy not only what humans know about catching Zzz's — but also the very idea of what sleep really is. 

Nocturnal animals that hunt “anything they can fit in their ample mouths,” American Bullfrogs can often be found resting during the day, a state that appears to be sleep to the untrained eye. But in reality, ”sleeping” Bullfrogs are just as ready to strike at a food source or flee from an enemy as they would if their eyes were open and metabolism heightened. In fact, its sleep patterns so closely resemble waking rest that some scientists have concluded the Bullfrog survives predators by simply eschewing rest altogether.

In a paper titled “Is Sleep Essential?,” published in the journal PLOS Biology, Chiara Cirelli and Giulio Tononi of the University of Wisconsin define sleep as “a reversible condition of reduced responsiveness usually associated with immobility.” What distinguishes sleep from resting wakefulness is the inability to react to external stimuli, and what distinguishes it from a coma is its reversibility. But with species such as the American Bullfrog, scientists seem to be unable to distinguish the difference between silent wakefulness and sleep, preferring the noncommittal term “rest” to describe the amphibian's habits.

The reason for this confusion is simple. A 1967 study by J.A. Hobson, still one of the only scientific forays into the nightlife of the Bullfrog, determined that the amphibian did not sleep “because even during the resting phase, they never failed to show a change in respiratory responses after painful stimuli.” 

Bullfrogs, according to Hobson, never actually fall asleep. Like an overweight uncle after too much Sunday dinner, they're “just resting their eyes.” The difference is that for the frog, the sentiment isn’t just a fib told to keep the Detroit Lions game on — it could be a fact of life. While sleep researchers like Cirelli and Tononi insist that more studies are needed before we can say for sure whether Bullfrogs actually do go without sleep entirely, the fact remains that even during their periods of greatest dormancy, the amphibians are still able to respond to the outside world should it impose itself.

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Much like the bright colors utilized by its poisonous South American cousins, this constant level of relative awareness keeps Bullfrogs safe from predators. By resting in the way it does, the Bullfrog is able to slow its metabolic rate, conserving energy just as creature who sleep more traditionally do while maintaining enough of a connection to the waking world to keep itself safe from its myriad predators — including humans, who hunt the amphibian for its legs.

Whether or not the Bullfrog really does go its entire life without achieving a deep sleep may need to be examined further, but one thing's for sure: the big-eyed amphibian's head is constantly on a swivel.