Never Kill A Boy On The First Date - S1-E5
Other mistake: In the famous scene where Buffy tells Giles, "If the Apocalypse comes, beep me," she grabs her pager from out of shot. Trouble is, she's standing in the middle of her hall and there's nowhere she could have picked the gadget up from. (00:21:00)
Other mistake: When T.J. types in his height instead of Floyd's while searching for his dad's date on the computer, he never pressed the "Enter" key.
Other mistake: At the start when the Lexus is found it is shown as a mirror image as can be seen by the badge and registration number. (00:03:57)
Gentleman Thief's Murder: File 1 - S1-E10
Other mistake: A single wimpy guy on his own wouldn't be able to bury something as large as a painting in a rush without leaving any trace the police can discover.