When J.D. is brushing his teeth and finds his brother is back in the bath tub and screams he has foamy lips from the tooth paste. However, when the shot cuts his lips are relatively clean again.
When Ted pulls his ice cream biscuit out of the trash and begins picking at it the amount and shape of what has been removed alters from shot to shot.
During the first scene we see Dan in the bathtub. He starts and for a split second you can see he's wearing Speedos instead of nothing as later scenes imply.