Continuity mistake: When Melvin and Carol enter the restaurant on their trip, a certain song is playing (I can't recall the song). Melvin leaves to buy a jacket, returns, and just after they are seated, you hear the female band leader say, "Here's a special song for...", and it's the same song they played 10 minutes ago. (01:34:00 - 01:38:15)
Continuity mistake: Simon's cut on his lip is quite visible in the car on the trip down to Baltimore and on the way back to New York, but it miraculously disappears while they are staying in the hotel in Baltimore.
Continuity mistake: In the restaurant scene with Melvin and Carol, when she is taking her drink from the bar to their table with the help of a waiter, when she first picks up her drink there is very little in it, but when she takes the drink from the waiter and places it on the table it is practically full. (01:33:25)
Continuity mistake: Before Carol takes a bath she tries to help Simon out of his shirt. In spite of being handicapped by his cast he insists on doing it by himself, although with difficulties, but he would never have managed to get out of his black pants into his jammie shorts between shots. (01:41:40)
Continuity mistake: After Simon has to dismiss his housekeeper, she is leaving the apartment with her large purse in one hand and several carrier bags in the other. She then lifts her hand, which is now empty, and says, "But who's going to walk Verdell?" There was no time for her to shift or drop her purse.
Continuity mistake: After the trio's arrival in Baltimore, Carol is in her room placing a call home. When she is first pictured placing the call she has a pager clipped to her jeans. It is gone, never to reappear, in the next shot. (01:30:40)
Continuity mistake: In the scene where the three of them are driving to Baltimore, Carol has a zit on her face. In the next shot it is gone. (01:26:20 - 01:27:30)
Continuity mistake: When Simon comes to Melvin's apartment to tell him that he has found his dog and Melvin tells him not ever to knock at his door, not even when the smell of a decaying body is emanating through the door so that he has to put a hanky to his face because of the stench, the glasses he is holding in his right hand disappear and reappear between shots. (00:07:20)
Continuity mistake: In the scene where Simon is sketching/drawing Carol, he rips off the hand piece of his cast so he can move his hand freely. When they are getting out of the car once they get home, you can see that the hand piece of cast that Simon ripped off is back on his hand and the cast is undamaged. (01:49:30 - 01:54:40)