Ferrets are usually as quiet as rabbits. When they get excited, they often do a "happy dance" and make sounds very similar to that heard in the movie. However, the "whining" sounds from the ferret behind the closed door are not normal.
The first time Reuben walks up to Polly when she is outside her apartment he runs across the road with no cell phone in his hand. When the shot switches to her then back to Reuben, he has his phone in his and is faking a phone call.
When Reuben and Polly are at the Mid-Eastern restaurant, Reuben is perspiring profusely; his face and shirt are soaked with sweat. When they go to her apartment, his shirt is dry and seems freshly pressed.
When Reuben is playing squash with Van Lew, Van Lew looses a tooth. Reuben says "You are bleeding" and we see as Van Lew reaches into his mouth that a tooth is missing then when he pulls a tooth out he has a perfect set of teeth.
When Polly and Reuben are arguing in the boat, equipment can be seen reflected in the television on the wall to the left of Polly. This cannot be Reuben because he is completely opposite of Polly at the time.
In the beginning of the movie there is a shot of an airplane landing at the St. Barts airport on a runway with a displaced threshold (area of runway with arrows). St. Barts does not have a runway with a displaced threshold.
Polly asks Rueben if he wants some more "bulgoki". Then she hand's him something green and leafy. This is done with the implication that it is more Indian food. Bulgoki is a Korean marinade traditionally used with rib meat and served with rice.
The goof items below may give away important plot points.
In the last scene, when Polly and Reuben finish talking to Claude, they wave at Leland in his boat just off the shore. Immediately after, they are walking toward the sea, with no boats in sight and the sun setting.