Other mistake: After the veterinarian throws blood all over the floor, we see clean spots appear on the floor in the shape of Sebastian's feet as he walks through the blood. Somehow he never has any of it stick to the bottom of his feet (even when he's in the puddle).
Other mistake: Elisabeth Shue uses the blowtorch to set off the fire sprinkler in the hallway, but later there is a raging inferno in the lab with all the important data and equipment and there's not one sprinkler, nor any alternative "electronic equipment friendly" automated fire suppression mechanism such as Halon gas.
Other mistake: During the scene when Elizabeth Shue burns Kevin Bacon with the flame thrower, she has blood on her shirt. When she shoots the sprinkler head the blood is gone.
Other mistake: The deadbolt lock on Rhona Mitra's apartment door is installed incorrectly, with the key hole on the inside and the lever on the outside. (00:57:25 - 00:58:05)
Other mistake: When Sebastian starts thrashing around he breaks restraints strong enough to hold an adult gorilla.
Other mistake: How does Sebastian breathe? He has a full head latex mask which covers his nostrils and doesn't have holes cut out. Many times during the film he has his mouth closed for long periods and has no way of getting air! He even eats a Twinkie without breathing.
Other mistake: When the subject is invisible, and the crew are attempting to return it to normal, when they inject the orange anti-serum into both the gorilla's and Caine's bloodstreams, it makes a noticeable "slooshing" noise as it rushes through their veins, which, technically, should make no noise at all.
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.