Factual error: It is not possible to be "allergic to all known anaesthetics". Amongst the amide local anesthetics lidocaine, prilocaine, bupivicaine, mepivacaine and dibucaine are naturally occurring substances and if administered without a preservative they cannot trigger an allergic reaction. If Bales is allergic to them, he'd be allergic to the metabolic processes of his own body. They are all powerful local anaesthetics and could easily be used for a radical rhinoplasty such as that required by Bales.
Character mistake: When Charlie is making the come back against the guy in the bar, he only needed twenty but he actually gives 25. When Charlie asks how many so far a guy yells out 14, but he's actually at 19 at that point.
Factual error: When they are putting out the fire, Charlie belts out "I want two 2-1/2 inch lines from the pump to the fire and three 1-1/2 inch lines from the hydrant to the pump". This is backwards. No fire department would ever use three small handlines to supply an engine from a hydrant.
Continuity mistake: When Roxanne finds out the Charlie is the one writing the letters, she pushes him out the front door and when the camera angle changes to the outside she's pushing him again about 3 feet away from the front door.
Continuity mistake: When Charlie is helping carry the telescope up the stairs, his grip on the telescope changes throughout the scene as the view changes from up close to far away.
Continuity mistake: When Charlie is going through his comebacks with the guy in the bar, right before he gives the last one he is seen from a distance standing next to the guy, then he starts and the scene changes to a close up and he is now leaning against the table that's up against the wall.
Continuity mistake: The soot on Charlie's face from the fire at the barn changes from when he's at the party to when he's on the roof.
Factual error: Early in the movie, CD and Roxanne are carrying her telescope up an external stairway. The scope is what is called a Newtonian, it's on a German equatorial mount and it's fully assembled. If she really were a professional astronomer she would never attempt to carry the scope assembled to the fragile German equi. mount. It is very easy to dismount the scope, carry it up separately from the mount, then reassemble up top. This would significantly reduce the possibility of damaging the very expensive mount.
Continuity mistake: Right before the barmaid hands Chris the cards to play lowball she just gave him his beer and then she has the cards in her hands.
Continuity mistake: When Charlie is talking to the kid on the roof, the kid's left hand is under his chin in one shot then on his cheek the next.
Continuity mistake: When Chris walks into the restaurant with the 3 girls at the table and he runs into the bathroom, watch the girl eating the sandwich. It keeps switching between hands. It starts right before he walks in.
Revealing mistake: After CD has swoon Roxanna for Chris, Charlie falls out of a tree in front of the old ladies. If you look close you can see a darker patch of grass that CD falls in. It's clear it's placed there as a soft landing pad for the stunt man to hit.
Revealing mistake: There are several scenes where the line where the prosthetic nose ends is very obvious: when CD goes up a hill to find out Roxanne is in love and when he buys make-up, for example.