Revealing mistake: When Spencer Tracey backs his car into the hotrod at the ice cream stand, you can see the hotrod already has a sizable dent before the car makes contact, probably a result of a previous take.
Continuity mistake: Towards the end of the film when Spencer Tracy and Katharine Hepburn are in their bathroom talking, Spencer is in the process of shaving. At one point, you see his face covered with shaving cream. When it cuts to Katherine and then back to him, the shaving cream is spread differently on his face. When it cuts to her again and back, it is different again.
Continuity mistake: In some scenes Katherine Hepburn wears a dress with a sash over her shoulder. First, when the Monsignor arrives and she makes him drink at the mini bar, and then later, when Spencer Tracy is giving his big speech. That sash repeatedly alternates between being folded and unfolded, and changes how it lies on her shoulder.
Continuity mistake: When Hepburn and Tracy park their car at the drive-in parking lot and order ice cream, the same large white truck (going left) and the same station wagon (going right) pass by on the street behind them three times. On this same loop there is also a white car that twice pulls out into the street going left.HuskyMiller
Revealing mistake: When they leave the studio to get into the taxi, there are multiple onlookers in the shot watching the scene from across the street. (00:06:00)