When they're driving over a long hilly section of the road and we see them coming at us, there is a line in the middle of the road. When the camera is behind them, there is no line.
By jerking the shaker his way 4 times, Joe E. Brown has dumped quite a bit of salt on Bela Lugosi's back. But as he gets up to fetch a postcard, the camera cuts to the opposite side of the counter where they're sitting; as Bela spins around on his seat, to follow Joe with his eyes, we can see that Bela barely has any salt at all on his back, even before he's started dusting himself off.
At the hotel restaurant, Aunt Polly unfolds the napkin and places it on her lap twice between shots.
Joe E. Brown asks Bela Lugosi's Pancho Arango what country he is from. Pancho replies proudly: "South America!" Of course, that isn't a country but a whole continent. It is unclear why the writers thought it was the kind of answer Pancho Arango would give, instead of naming one.