Pet bites are a big problem. Dogs bites in particular are far too common and can result in serious injury or even death in a small percentage of cases. Bites from other pet species also happen, but the extent of the problem is not clear. A good general rule is if it has a mouth, it can bite.
Another good general rule is if it has numerous sharp teeth, is a carnivore and your as upsetting it, you should get your hand out of the way. Pet store owner Dave Brown found this out the hard way, although in this situation he has the dubious distinction of having been bitten by a fish.
It seems that Mr. Brown was trying to catch a piranha that he was selling. I would have thought the standard way of catching a fish, not to mention a six-inch-long carnivorous fish, would be to use a net. Apparently not. Mr. Brown used his bare hands, and after a couple unsuccessful attempts to catch the fish, the piranha fought back, sinking his teeth into the store owner's thumb. The bite was severe enough that stitches were needed. According to Mr. Brown "There was blood everywhere. Every time I had him in a plastic bag the fish would bite through it. He was quite a feisty one." Personally, I think if a carnivorous fish was repeatedly trying to attack me through the bag, I'd probably change my approach to catching it.
According to a local fish expert, "[Mr. Brown] was very unlucky as these fish normally just attack when they're hungry. It may have been a bit peckish."
Fortunately, apart from a sore thumb, it sounds like the biggest problem Mr. Brown will face is the harassment that I assume he's going to take from friends after being bitten by a fish.