(and no Tom this isn't a half-joking warning ;) )
http://news.nationalpost.com/2014/09/05/vicious-beaver-attacks-halifax-snorkeler-off-nova-scotias-coast/
(http://wpmedia.news.nationalpost.com/2014/09/na0906_beaverattack_c_jr.jpeg?w=620&h=742)
(their tooth is almost as big as a Great White Shark ... and in one of the comments they tell of a sad tale of a man actually DYING from a beaver bite in an artery in his leg (http://www.theguardian.com/world/2013/may/29/beaver-kills-man-belarus)(!) )