What is the penalty for calling rummy when your hand is wrong in gin rummy?

Well, honey, if you call rummy with a wrong hand in gin rummy, you're gonna be hit with a penalty. The penalty is that you have to add up the value of your opponent's deadwood in their hand and add it to your own score. So next time, make sure your hand is on point before you start shouting "Rummy!" like you're at a bingo hall.