Plot hole: Kate is in the future and has named the dog Jack and informs Alex of this in a letter, which he receives in a magic time-travel mailbox. Alex adopts this same dog in the past, before the dog has ever met Kate. Jack tests out the name "Jack" on the dog, and the dog reacts to this name. The dog should not know this name as it hasn't yet met Kate. This is backwards. Alex should have been the one to tell Kate of a name he gave to the dog, and she should have been the one to test it on the dog.Uncel Mark
Plot hole: At the end of the movie, when the water drains away, there would be no way for a) the amount of water to drain away that did and b) for the mammoths that came through to be completely dry. (01:16:20)
Plot hole: When Farley is preparing to rescue Simon by towing him up with the rope attached to his van, he drops his "cigarette" into his crotch, causing him to floor the gas pedal. His back wheels begin to spin. This is impossible because the vehicle is still in Park. There is even a camera shot of the "PRNDL" proving this. I guess this goof is employed by the filmmaker to increase the dramatic effect of him subsequently slamming the Dodge into drive a second later and careening through the fence. (01:07:35)
Plot hole: When Melvin receives the phone call from a lost Diana, he is staring at his goldfish, swimming peacefully in the bowl in his apartment. He unsuccessfully attempts to rescue Diana, then goes to the night club where he encounters an inebriated Ginger. He escorts her home, rebuffs her advances, and goes to his own apartment. The next morning, he goes to her job site, where, inexplicably, the goldfish has now taken up residence. Unless Ginger's flunky somehow broke into Mel's apartment and absconded with the fish, there is no way the fish could have gotten there on its own.
Plot hole: Viola convinces her mother she is staying at her father's house for two weeks, but who covers for Viola with school administrators? As far as we see in the movie, Viola is not reported absent from either Cornwall or Illyria (a transfer would explain not being reported absent from Cornwall). Administrators or class mates at Cornwall would find it strange that she stopped showing up, since soccer training had already started. It is unlikely Viola officially transferred to Illyria, since her parents would have to sign off on that, or at least start paying her tuition to a different school. Viola could have called in sick to either Cornwall or Illyria, but this is never addressed in the movie. And if the soccer program at either school started before the official school year, it would make no sense for them to have a biology class with students not enrolled in athletic programs at Illyria.
Plot hole: Just before the bomb explodes at the beginning of the movie, the guard is looking for the car playing 'don't worry baby' on it's stereo. In the final timeline the disaster has been averted, the bomb having gone off, and the ferry docked. After this, when Carlin is in the car, the same song is playing, but the bomb was set to a timer.