It's a birthmark.

I promise never to exhibit these in publ… What valuable conclusion can be gained f… Now you, Todd, can either help me out or… Rosie, there's a tattoo on your ass. The traitor in our midst. You know, a lot of people think history… They said. New friend is not to fidget either. It seems to be some sort of garden based… Milo, this is another whinging story abo… And if we can prove you killed it it's y… It's up to you. Well, there shouldn't be violence. Stop playing that bloody game. Tell this man we're civilized people.