What do octupi become stressed about? The answer is at 11!

Stressed Octopuses can sometimes suffer from autophagy, or self-cannibalism. That is what is described as "eating its own arms." It is believed that it is caused by a virus/bacteria which can manage to take hold on a stressed octopus. The biting is said to be due to irritation and biting alleviates the affected area. An octopus can lose an arm without harm and regrow it.
-http://en.wikipedia.org/wiki/Self-cannibalism