When the rattlesnake is shown first from behind, its tail is close to a foot behind its head. When the angle switches to Joe's point of view, the tail is now beside and almost in front of the head.
Greg Morris picks a whole bunch of small berries and hands them all to Mannix. They are small enough to fit in both his hands---unseen. The next frame, Mannix has a huge green grape in between his teeth. Besides size discrepancy and all, grapes don't grow on tree branches.
When Mannix first wakes up, in the sun, the bandana on his bicep looks exactly like what it really is: smeared with caked-on vermillion paint, instead of looking like dried crimson blood.
The action was supposed to be in New Mexico, but the Plymouth sedan belonging to the people in the farm house had California plates.