Well, here's something you don't see everyday.

This snake in a pet shop was recorded eating itself. Instead of finding someone to make it stop, some dude decided it would be better to record it. While this phenomenon is rare, it does happen when snakes get disoriented or stressed. According to this article at iflscience.com:

If snakes get too hot, they can become confused and disoriented. They also get a ramped-up metabolism, causing them to have a false sense of hunger and a desire to eat the first thing they see. As captive snakes typically live alone and food isn’t routinely consistently available to them, they end up attacking themselves.

The article goes on to say that it is possible to get the snake to stop eating itself by turning down the heat and spritzing it with cool water, but most of the times, these instances become fatal.