Continuity mistake: The T-1000 has the gun holster on his left side and takes the gun out with his left hand when the guard in the psych ward hits the alarm. A few scenes later when the T-800 (Arnie) asks Sarah to 'come with me if you want to live' the T-1000 walks through the cell doors, the holster is on the right hand side and the gun in his right hand. (01:10:00 - 01:12:00)
Other mistake: As the cop is walking towards the coffee machine, he steps on the T-1000 (disguised as the floor). The cop proceeds to the coffee machine and buys a coffee while the T-1000 turns into the cop. The T-1000 only touches his shoe, so shouldn't be able to copy his appearance. (00:51:00)
Other mistake: When Lewis looks at the cup that he got from the coffee machine, the cup has two Jacks and two Aces. When he looks at the bottom of the cup, it has a Queen underneath giving him two pairs, but he tells Gwen the receptionist that he got a full house.