Corrected entry: Seth is using a cream made of green (i.e., kryptonite) roses to make himself invisible. At the beginning of the episode, Clark is in the locker room and feels ill from the kryptonite rose cream that Seth is wearing as he beats up the kid who picked on Amy. For the rest of the episode Clark does not feel the effects even though Seth is close enough to him at least two other times in the show. Once after Seth trashes Victoria's room and runs past Lex and Clark and again when Seth tries to drown Victoria in the tub.
Corrected entry: Clark realizes that Amy stole Lex's watch when he sees her wearing it. He and Lex then search Amy's room with her mother and find the watch. Amy wears the watch as a token of her obsession and would not take it off lightly, even if she had returned home and left again.