When Guido visits the cardinal in the mud bath, the cardinal is sitting in a chair, fully dressed in his cassock, as two attendants use a sheet to form a curtain around him; however, as the camera cuts to a closer angle, the cardinal is suddenly undressed to the waist.
When Guido visits Carla during her illness, a strap of her slip disappears in the close shot after she rolls over, but is apparent in longer shots both prior and after.
When Guido and Claudia go out for their drive, they stop near some springs. Guido exits the passenger side of the car (off camera); we hear the door open and close. But when Claudia, who was driving, steps out moments later (also off camera), we never hear her door open or close.
When being gassed on the ferry boat, it's odd that the man doesn't even try opening one of the wing vent windows. Those are simple hinged windows. As the owner and driver of the car he would know this.