During the credits the spelling of Rennard's name changes. It is spelled "Rennard" when referencing the living character, but the undead character is spelled "Reynard."
When Brother Silence says "Where's he gone?" in the fight with Mort Kemnon, Flynn puts his lute in the right hand (the one that was bitten off by Lodge's cat). However, it is back in his left hand for the shot in which the prop right arm falls off.
When Sir Osric is being electrocuted at the end, when the camera pans back to Daphne you can see Flynn holding his mandolin. When it pans back to Flynn after Osric dies he is not holding it anymore. He picks it up to start playing.
The party is playing D&D 3rd edition and Leo/Flynn mentions he has 20 ranks in seduction. However, at 9th level 13 ranks would be the max.
When Flynn the Fine discovers the secret passageway, and loses his arm (that has been severed by the cat), one can see his real hand in the shoulder-hole of his tunic, releasing the fake arm to allow it to fall to the ground.
After the last session of the game, Kevin is shown typing on his computer actually writing his story, wearing his brown leather jacket... yet the session was at his house and he was only wearing a t-shirt. There are two views to this scene: the close up from over his right shoulder with him wearing the jacket, and a long shot from down the hall looking over his passed out roommate with Kevin no jacket just t-shirt.