In the reverse angle of Tim looking into the microwave, you can see there is no wall opposite the microwave. (This is where the audience sits)
Before Tim looks into the microwave you can see the small camera that has been set up inside the microwave to capture Tim's face. You can see the bar that the camera is mounted to when Jill opens the microwave.
When Brad and Randy are in Wilsons Garden asking about Clifford you can see the studio camera being moved on other side of the fence.