I know snakes can unhinge their jaws when they eat food that is large (rats, large mice, etc.), but I don't know how much that helps them to open their mouth. How wide can adult corn snakes open their mouths when they eat?

Recently I noticed my pet corn snake's mouth was really wide when he was eating a huge rat and I was concerned that it may have been too large for him to consume safely.

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    I think pet owners looking for reassurance on this subject, having seen their snake eat something that is apparently far too big to fit in its mouth, will come to the pets site rather than the biology site. A question (or answer) about how the snake's jaw structures correlate with the structures of the inner ear in humans would, however, definitely be right for bio. – ClickRick May 29 '14 at 17:15
  • Please note that "maximum angle of mouth opening" shouldn't be the metric for choosing an appropriate feeder rodent... – SuperStew Jan 4 '19 at 23:34

In general, snakes can open their mouths at about a 150 degree angle. That's pretty amazing when you consider 180 degrees is a straight line!

The reason that snakes can open their mouths so wide is that their jawbone is connected by ligaments, rather than hooking into the skull like other animals.

As you can see from the human jawbone below, the connecting points make a 'U' shape. That allows the jaw to rock back and forth (open and closed), but the movement is extremely restricted to the connection to the skull and facial muscles.

Human Jawbone (Source)

Compare this to a snake jawbone. The snake's jawbone really isn't connected to the skull in nearly the same way. Rather than a (for lack of a better term) physical connection, the jaw is connected through ligaments and tendons.

The "small bone" is connected to the back of the skull, and the mandibles are connected to that. This allows for the snake to drop its jaw further than if the jawbone was hooked into the side of the skull. It also doesn't really "break" it's jaw. Rather, the tendons and ligaments that hold it all together are fairly stretchy, allowing even more movement.

Snake Jawbone (Source)

Another fun fact about snake jawbones is that the mandibles aren't fused together like human jawbones are. Human jawbones actually start as separate mandibles, with cartilage in the chin, but the cartilage fuses into bone as the person grows older.

Snake mandibles are (like the connection between the jaws) connected by tendons and ligaments, so that their bottom jaw can stretch wider if needed. Though that is used more for wider prey, or even eggs.

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  • This explains it. My corn snake was eating a huge rat and his mouth was open so wide I thought he is dying. – Blender Warrior May 29 '14 at 14:59
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    @PsychOPhobiA It is possible for a snake to try to eat something that's too big for it. The general rule is to only feed your snake a rat/mouse that's the same size as your snake's body is at its widest point. – Spidercat May 29 '14 at 19:51
  • @Matt That was the rule of thumb I'd been given by breeders and other keepers, but one of the UK's reptile food suppliers suggests it should be 1¼x or even 1½x. – ClickRick Jun 4 '14 at 22:30
  • @ClickRick I've heard that as the maximum size. Although I've also heard it used in reference to the size of the head, which for some snakes would be the size of their widest point. I stay a bit under the maximum size to be safe, if the size of rodent you get happens to be a bit bigger than expected it's not as big of a deal if you were planning on it being a bit smaller than the maximum size to begin with. – Spidercat Jun 4 '14 at 22:43

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