They'll do that when they "move" around. They're attached and don't move quickly but they are capable of moving some and when they do, they'll leave a little piece of their foot behind and it'll sometimes grow a new stalk. Once it gets a little bigger, you can remove it with a razorblade and give it away or place it somewhere else in your tank if you want. I have a whole colony of superman mushrooms that started out at 2. As they migrate in or out of light, new one's pop up. Rright now I'm looking at 9 separate mushrooms.