They strike with the force of a small caliber bullet, so thats how they can break glass. They get into your tank by hitchicking on liverock. They can survive for long periods of time with less than good conditions. And yes, they can harm humans. Divers and fisherman have dubbed them "thumbsplitters" because if you happen to accidently come across one it could easily slice your finger open. With that said, I think they are pretty cool, and if they weren't so reclusive I would think about having one.