Using this technique creates a stale cockatrice egg on the player's location, or sometimes several if the technique's level is high enough and the player is lucky. It will then have a random timeout of about 2000 turns. Picking up the egg(s) is not dangerous for a rocker thanks to intrinsic petrification resistance, but other roles should make sure they're wearing gloves. The game will also display the message "You create some stoning grenades."
Don't use the egg bomb technique if you're blinded, wearing no gloves and lacking petrify resistance, unless you absolutely know what you're doing!