A friend of mine has a tank with some neon tetras, guppies and a snail. One of the guppies started to kill the tetras and the other guppies by fighting them and stopping them from feeding. It killed all but one tetra which they named slippy because he "slipped" away from the killer guppy. Then the guppy then hopped the twig too. Is it common for guppies to act like this? They got the fish in a massive fish-only pet store which is very good.