Revealing mistake: Somebody has already pointed out that the footage of Deeds throwing the cats out of the window is obviously not caught on Pam's camera. In addition, notice that there is no guttering/pole to the left of Mrs. Keeling's flat window - it is on the right. Yet on the TV footage, there is a metal pole to the left of her window. Another point is that Mrs. Keeling's flat is on the corner of a street, yet when we see footage of the cats flying out of the window, her flat isn't at the corner of a street, it's in the centre of a row of flats.
Revealing mistake: When Jan and Pam are fighting, you can tell for most of the stunts Winona Ryder isn't doing them, and it's a double. For instance when she runs into Jan, and gets knocked to the floor, and when she gets thrown into a table. This is confirmed on the commentary too.