Visible crew/equipment: When the baby in the baby stroller is rolling down the cliff hills, a safety wire attached to it is briefly visible, as Luke chases after it.
Visible crew/equipment: The scene where Luke is changing into a mouse, you can see the masking tape on the floor where Anjelica Huston's feet are supposed to be positioned.
Visible crew/equipment: When the witch throws the toy airplane back up to Luke, who is standing in the treehouse, a wire is visible attached to the airplane, guiding it up to him.
Answer: We've already witnessed Bruno being turned into a mouse so there's no need for us to see Lukes transformation as we already know how his transformation is going to be.