Stupidity: When Dr Loomis and Sheriff Bracket are chasing who they think to be Michael Myers, you can tell that it isn't him. Michael Myers is supposed to be 6'2 - Ben Tramer is maybe 5'4. If Michael was shot 6 times there would be blood on his overalls. And the mask that the kid is wearing has blonde hair, whereas the mask Michael wears is brown.
Stupidity: The sheriff kneels down to examine Michael's 'body' as the doctor yells at him to get away, and the sheriff tells him Michael stopped breathing. Michael suddenly grabs the sheriff and throws him onto the ground and raises the scalpel to kill him. The doctor aims his gun at Michael to shoot him but doesn't, when he had the opportunity before the sheriff is killed.