What sets Homo sapiens apart from other animals? Among other things, our chins do. That piece of bone sticking out from your jaw is somewhat of a mystery - one that's inspired a diversity of wild theories to explain its purpose, according to a paper published this month in Evolutionary Anthropology.

The author of the paper dismisses a number of these explanations, such as the possibility that the chin serves as a sexual signal (such traits usually only appear in one sex - like the mane of a male lion). Another proposal is that the chin acts to protect your throat - an idea the paper's author also shoots down, because for this to be a substantial advantage, humans would have to be constantly punching each other in the face.

So the mystery rem ...

Rattlesnakes are a group of venomous snakes native to the Americas known for their loud rattling tail. The tip of their tail, known as the rattle (middle), vibrates to deter predators or serves as a warning to passers-by.

The rattle is composed of a series of hollow, interlocked segments made of keratin, which are created by modifying the scales that cover the tip of the tail. The contraction of special "shaker" muscles in the tail causes these segments to vibrate against one another, making the rattling noise (which is amplified because the segments are hollow) in a behavior known as tail vibration. The muscles that cause the rattle to shake are some of the fastest known, firing 50 times per second on average, sustained for up to three hour ...