Timberly Loves Arnold / Eugene, Eugene! - S5-E22
Trivia: In "Timberly Loves Arnold", when Timberly shows Arnold her flower drawing, as Sid says, "Look, it's a flower named Arnold," part of his shirt is invisible in the first frame of the shot. This can only be spotted in slow motion or with pausing, therefore it's under trivia. (00:02:22)