Audio problem: At the beginning, when they steal the dolphin, you hear the peel-out sound effect as if the truck was on a paved road, but they were on grass.
Continuity mistake: When Ace is in the asylum, he is trying to hide in a little cardboard box from an employee of the building, so he crams himself into a box and when the man leaves he breaks out of it. He ends up completely squishing the box underneath him. When the camera comes in for the close up shot, the farthest side of the box from the viewer is now undamaged.
Continuity mistake: When Ace is sneaking into Ronald Camp's Private Aquarium, he begins to look around and open some doors. If you look at the colour of the wall it is red. When he opens the door to the giant tank, the wall outside the door (which should be red) is now white. The door also reverses - the handle goes from Ace's left to Ace's right.
Deliberate mistake: In the scene in which Ace is in the asylum, he breaks into a storage closet to view Finkle's belongings that were left behind when he escaped. At first the doorframe is such that the door closes against about an inch of wood, meaning the lock would be behind this wood, so Ace couldn't pry it open. In the closeup, the door's flush against the frame so Ace can use the sign to get between the door and the frame. In the wide shot it's back to how it was.
Continuity mistake: In the apartment crime scene, Sean Young says "we'll let you know if we find a tic", and the large grey-haired cop on her left chuckles, arms by his side. We then cut to a close-up of him with his hands on his hips, pushing his jacket to the sides, then back to the original shot with his hands by his sides again. The close-up itself is a bit weird - Sean Young should be right in front of him, but isn't visible. They must have used a later shot, because after about a minute, when everyone's moved around a lot, we see him back in exactly that position, only now the people visible fit the scenario better.
Factual error: When Snowflake is being stolen at the beginning, he makes the high-pitched noise that dolphins make even when he is out of the tank; those high peals are made underwater through carrying sound. He wouldn't sound the same out of the water as he did under it.