(at around 34 mins) We see worms in Billy's hands. Those worms were supposed to be in his pants because he lost the bet. As Billy runs out of the school he is seen putting the worms in his pocket then removing them.
After eating the spicy worm at Twitch's house, all the boys are waiting outside and Twitch runs out, slams the door, turns the lock and says: "No more cooking in my house!" Doors don't lock from the outside.