"Yawn" derives from the Old English words 'Ginian' and 'Gionian' meaning to "open the mouth wide, as if to gape." It is a reflex action of simultaneous inhalation of air and stretching of the eardrums, followed by exhalation of breath. In man, it's commonly associated with tiredness, stress, overwork, lack of stimulation and boredom, though recent studies show it may be linked to the cooling of the brain. However in animals, there are a number of reasons why certain animals take to yawning.

Sometimes used as a warning signal, baboons yawn to threaten their enemies, possibly to prominently display their rather large canine teeth. Similarly, Siamese fighting fish yawn when they see a conspecific (same species) or their own mirror-image, and their yawn often is accompanied by an aggressive attack. Guinea pigs also yawn in a display of dominance or anger, displaying their impressive incisor teeth.

Adelie Penguins employ yawning as part of their courtship ritual. Penguin couples face off and the males engage in what is described as an "ecstatic display," opening their beaks and pointing their faces skyward. This trait has also been seen among Emperor Penguins. Researchers have been attempting to discover why these two different species exhibit this trait, despite not sharing the same habitat. Dogs often yawn after seeing people yawn and when they feel uncertain.

Tastefully Offensive is a humor site that delivers a daily round-up of the funniest photos, memes, comics and videos found on the Internet.  In this mash-up production, they compiled a wide variety of animal species known to yawn. Pulling from existing YouTube vids, check out the pandas, cats, polar bears, koala bears, leopards, monkeys, otters, seals, turtles and even a yawning corn snake named Leo. [Note: It is said that snakes yawn, both to realign their jaws after a meal and for respiratory reasons, as their trachea can be seen to expand when they do this.]

[Warning: This video can make the human species known as man, very sleepy!]

Perhaps the most famous animal caught in a yawn was Leo the Lion, the mascot for Hollywood's Metro-Goldwyn Mayer film studio. But was it really a yawn? Many ascertain that this famous lion was actually roaring -- not yawning.

Here's two lions demonstrating first hand how yawning can definitely become contagious.

Now compare those yawns to MGM's Leo, first played by Slats at the opening of the 1924 movie, "He Who Gets Slapped." Not only does this lion not yawn, he doesn't even open his mouth. Perhaps this was because it was a silent movie.

Replacing Slats, Jackie assumes the role of Leo by lending her unique style to the famous sound we associate with MGM, even to this day. And just in case, you still think it's a yawn versus a roar, she repeats herself three times as if to say, "I'm not bored or tired folks, so you better be paying attention."