Continuity mistake: At the end when Sheldon has got a burger, the amount of burger left changes depending on the camera angle. Most noticeable when he asks Penny about permanently reserving the table - between shots the lettuce disappears, the bun changes colour, and the bite marks change.
Add timeA Demon
Continuity mistake: When Raj is drinking with Lalita in the bar Penny works at, in one shot he raises his Grasshopper drink to his lips with his left hand. In the next shot it's in his right (this is just before he says "Oh my God, you've lost so much weight").
Continuity mistake: When Raj's parents tell him to put his laptop down and gather his friends, they all huddle around the one-seat sofa. Sheldon is crouched to the left of the seat with his hands on the sidearm, yet in shots angled at the left he has disappeared from his place (as to not obstruct these particular angled shots.)
Continuity mistake: When Penny asks Sheldon "What trauma?" in the electronics store, Sheldon holds two boxes - one with an orange side on top of one with a black side. In the next shot the black sided box is on top of the orange one. The boxes then continue to swap places during the whole scene.
Continuity mistake: When Leonard and Sheldon are talking with Penny during the scene where she is being allowed to sleep on their couch, the pullstring on her hooded jacket keeps alternating from hanging loose to being caught inside the top of the jacket.
Continuity mistake: When Sheldon walks out his bedroom wrapped in a comforter, he drops it on the higher level before the drop down to the kitchen. In the next shot as he walks away from the fridge, half of the comforter is now spread over the lower level without anyone moving it.
Visible crew/equipment: When Leonard, Sheldon and Penny are eating lunch for the first time, Penny sits on Sheldon's spot, Leonard then tells him to "Just sit somewhere else." He then walks over to his desk chair and contemplates sitting there and in the bottom left of the shot there is a chair with 4 false legs, and one large leg running down the middle.