Continuity mistake: After Jon 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. When Jon comes back into the room to turn off the stereo, the picture is suddenly back up on the table without him replacing it.
Continuity mistake: 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.
Continuity mistake: During Garfield's lasagna speech in the kitchen, the gourds on the table keep changing positions.
Continuity mistake: When we first see Odie on the double decker bus (about 22 minutes into the film), he is wearing a miniature souvenir "bobby" helmet. Then we see him chasing pigeons in the square hatless. Then the hat returns (did he have pockets to keep it in?). Then they are at a statue of Churchill - again he is hatless and we never see the hat again.
Continuity mistake: When all the animals are shown in the pool, the ferret is drinking the champagne. But Lord Dargis says that a bull was drinking the champagne. (00:51:25)
Continuity mistake: During Garfield's song at the castle, just after Winston shows him his room, the bell cord (the one Prince pulls when he requires something) disappears and reappears throughout the song.
Continuity mistake: Just after the reading of the will, we see Dargis and a group of tourists out the front. When Prince's cart passes behind Dargis, we should be able to see Prince, but we can't. (00:12:35)
Continuity mistake: Just before Liz rings the doorbell, the wine stain on the front of Jon's shirt changes shape repeatedly between shots, then vanishes altogether. (00:06:30)
