At one point during the band's performance of "Earache My Eye", the brass section can be seen not playing their instruments when they can be heard on the audio track, but in the next shot they are clearly playing along with the track.
When Cheech cuts across the road to pick up Chong, the two girls are seated on the bench waiting for their ride. When Cheech stops to let Chong in, the girls are already quickly loading their surfboards into a van that wasn't there when Cheech stopped.
After getting pulled over by the stoned motorcycle cop, the scenes repeatedly switch back and forth between Chong in the driver's seat to Cheech in the back of the truck with the girls where there is only a curtain separating them. But from the back, the view beyond the curtain should be that of bright daylight but is instead total darkness indicating the back of the truck is a set.