a puffer may do it randomly on its own without anything triggering it. when they willingly do it they are fine. but when they do it when they are threatened/stressed it isnt healthy for them
hate those lil things my ex girlfriend put a puffer in one of my tanks (cuz she thought it was cute) anyway it was a long time ago she got it from wall mart and put it in without me knowing, well my cichlid thought it was a meal and end up floating at the top of the tank with a puffer stuck in his throat i netted the dead fish which i was really upset about and almost instantly the puffer swam out like nothing sorry to all fish lovers like me but i killed the f&*%r never again will a 3 dollar fish cost me a 30+ dollar fish anyway this is one of the many reasons shes my ex i never went through her crap id appreciate it if she stayed the f*** away from mine