Visible crew/equipment: At the very start, Zack hands Billy some glasses which he puts on. They reflect the stage light in front of them perfectly. (00:01:10)
Visible crew/equipment: After the Iguana changes back, the camera pans up from the floor and you can see the camera shadow moving up Billy's leg. (00:18:10)
Answer: Probably to save on costs of filming the same scene. In the reused shots they have always morphed so you can't see the actors. They just have to pay them to do voice-overs rather than the entire scene.
Ssiscool ★