When Jon spills wine on himself due to the shock of sudden loud music, there are just a few drops of liquid on his shirt. however, when he goes to open the door for Liz, most of his shirt is drenched in front.
The castle tour guide states that the portraits of the past owners are painted by the Dutch master Anthony Van Dyck. Van Dyck was born in Antwerp, Flanders (in Belgium, not Holland) and thus was a Flemish baroque master painter.
When Dargis is talking to Liz in the kitchen, he is wearing a brown suit. He then leaves the kitchen in pursuit of Garfield, and the next scene shows him in a black jacket and gray pants. There was no time to change clothes.
After John tells Garfield that he is going to ask Liz to marry him, Garfield knocks Liz's picture to the ground and we hear glass break. In the next shot, we see Liz's picture on the table, and the glass is not broken.
When Garfield first walks into Carlyle Castle, the pattern on the tiled floor is black diamonds with white stripes. In the next shot, when Garfield is yelling, "Mom, Dad, I'm home," the pattern on the tiled floor changes.
When Prince comes out of the sewer, he's shaking some of the dirt off him. When it zooms out right when the humans come by, the dirt disappears, and then re-appears when it zooms back on Prince and Odie.
When Rommel is chasing Dargis after the animals fire the clay
launcher at him, Dargis falls to the ground and looks behind him. As Rommel comes bounding around the corner, there are three people visible next to a stone sculpture. The camera switches to Dargis, and when the camera goes back to Rodney, the people are gone.