My puffer will take a chunk out of my arms if I am aquascaping for too long- it's creepy- 2 teeth marks on top, 2 on the bottom and a circular beak bruise surrounding it, and yes, there is blood drawn. He's patient, though, he likes to be right under my hand when I reach in HIS tank to clean up things that he kills, but after an hour of playing with rocks he gets mad and starts nipping at my elbows. People have asked me on more then one occasion what is wrong with my arms, I laugh and tell them my fugu did it and walk away. He will not let anyone but me reach in his tank, he has jumped to try to bite my husband and several friends, mean little tiny thing!!