In the scene where Red and Chong walk into the music store, Chong picks up a Fender Stratocaster and starts playing. The camera cuts around the store and, when it cuts back to Chong, he is suddenly playing a Gibson Les Paul.
In the welfare office, the long string of numbers coming from the dispenser varies in length throughout the scene.
The amount of "coke" on Cheech's face in the van.
Chong mispronounces pendejo as "bendecko" and Cheech doesn't correct him. When they crash into the family's house, Chong calls them "Pendejos" correctly.
When Chong is urinating out of the open bathroom window, the
camera pulls back slightly and reveals that the "pee" is actually water running from a sponge being held just off frame. The crew member holding the trickling garden hose quickly pulls his hand out of frame, but not fast enough.
When Chong and Red are walking around the hotel with Red's luggage (just before the police sirens get their attention), the camera tilts and pans to keep them on screen. As the camera moves, shadows of the camera and crew become visible at the bottom left corner of the screen.
After Cheech and Chong remake their van and after jumping their van, you can see feet pushing the van.