Not sure how authentic it is, but here [1] is an explanation: > It is believed that it is caused by a virus/bacteria which can manage to take hold on a stresse

Not sure how authentic it is, but here [1] is an explanation: > 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. By biting it off, the octopus loses the infected arm and hopefully a healthy one regrows, but in captive situations, probably caused by bad water quality, the infection can't be shaken off. [1] https://tonmo.com/articles/do-octopuses-commit-suicide.47/ https://tonmo.com/articles/do-octopuses-commit-suicide.47/