Continuity mistake: Early in the movie, when Kevin Bacon and Josh Brolin begin to chase Isabel (the invisible gorilla) down the hall, Kevin does not have any special goggles and didn't grab any when he got the gun. This is confirmed when we see the backs of their heads as the chase begins. When Kevin catches up with Isabel, he brings down his goggles from the top of his head as if he had them all along.
Continuity mistake: When Linda and Matt are trying to escape from the freezer, the amount of blood changes on the door lock.
Continuity mistake: Matt is bitten by the gorilla on his hand in the beginning, but in the next scene where the gorilla is strapped to the table, his hand is fine. Shortly after the gorilla is made visible, his hand is suddenly bandaged.
Continuity mistake: In the early part of the movie when Sebastian is checking the stability of the molecule, you see the 3D molecule model explode and the separated atoms pause. When Sebastian turns away, you can see that the atoms are no longer on the same position.
Continuity mistake: When Kevin Bacon and Elizabeth Shue's boyfriend shoot the gorilla, the gorilla passes out. No one moves the gorilla, yet the red headed veterinarian walks right through the area where the gorilla passed out.
Continuity mistake: When Elizabeth Shue sets off the automatic sprinkler system on the ceiling, a great amount of water is spraying from each one. However, after Shue and Josh Brolin attempt to climb up the escape ladder through the elevator shaft, all of the water is gone.
Continuity mistake: The "tranquilliser guns" are really PGP paintball pistols. The little tube on top only has a little hole the size of a paintball you load it, yet in the movie they seem to hold a good amount of large darts in that tiny gun.
Answer: Do you mean the scene where he is invisible, wearing his mask? If so, the song is called Charlie Big Potato by Skunk Anansie.