When Sarah is in the car with Peter going for a drink, the scenery outside the car is different from what is shown through the back window from the inside view of the car.
When Sarah is sleeping in her wedding dress, a tissue is placed into her mouth; on the next shot, it's gone.
At the beginning of the movie, Sarah is pushed into a man who spills coffee on her. Seconds later, her shirt has no stain at all.
When they are stopped on the edge of the cliff, the old woman reverses into their car and pushes it over the edge. When the camera cuts back, the car is still in the shot.
When Tom throws his jacket onto the chair in the hotel in Venice, it is scrunched up. When he picks it up to leave, it is neatly laid across the chair.
The radio station Tom works at appears to be a recording studio, not a broadcast station.
When Tom and Sarah crash into a snow bank and they decide to spend the night in the car stuck in the snow bank. There is no way Tom and Sarah would've survived one night in a snow bank. They could've froze themselves to death as Sarah predicted.
Obvious stunt double used in the opening scene when Sarah falls over the trolley at the airport.
If you watch with CC/Subtitles. After Tom and Sarah crash into the snow bank and they try to sleep and Tom tries to back out. When Tom is mumbling to the steering wheel before it breaks off, the captions will say that he said "there's no fucking tilt wheel in Europe!" He only said "there's no tilt wheel in Europe" he doesn't say "fucking".
The castle/hotel is located in France (in fact, it is "Burg Taufers" close to Sand in Taufers, in South Tyrol, Italy). The Tyrolian Flag on the wall belongs to South Tyrol. Despite the fact that the cars have the correct French license tags, a local construction company's truck (Kiesunion) is seen on the highway. Also the electrical sockets in the bedroom are Italian, not French. The uniforms of the firemen coming out of the castle after the fire are clearly not French. (The helmets used by the firemen are former Wehrmacht helmets repainted in white and are commonly used by fire brigades in Germany, Austria, and South Tyrol but not in France.)
During the pan shot of the courtyard belonging to the castle hotel, which is supposedly in France, there is a visible Tyrolean flag hung in the courtyard. Tyrol is one of the nine provinces of Austria.
In Venice, Sarah is in a large rectangular room filled with paintings by Tintoretto (which she had earlier declared her desire to see) and then leaves, upon which she is accosted on the stairs by Peter. However, the room with the Tintorettos is in the Scuola Grande di San Rocco, not in the Santa Maria della Salute Church, which is where she is shown leaving. They aren't even in the same neighborhood. (And La Salute is in the shape of an oval and has no rectangular rooms.)
When Sarah is in Italy, in Piazza San Marco (with the pigeons), she's reading a guidebook that says "Florence & Tuscany"; however, she's in Venice, which is a city in the region of Veneto, not Tuscany.