When Caine injects himself with the fluid to make him invisible, you see bubbles going through the tube into his arm. These bubbles, once in his veins, would cause severe pain (though are probably not enough to kill him). Hence doctors in real life flick the bubbles to the top of syringe and squirt them out. At the least, a medical professional injecting air would be highly unprofessional.
When Sarah throws blood on the floor, her shirt hardly has any blood on at all. When she is about to put the remaining bag of blood back in the freezer, a few blood smears appear on her shirt. They disappear and reappear in between shots throughout the scene.
At the start, when Linda tells Matthew that they have to get to the lab, she is wearing a nightshirt and obviously no bra. However, when she sits down at the dressing table, bra straps suddenly become visible under the shirt.
When they put the reversal liquid into the ape a rubber band was used to help find the blood vessel. When they did the same thing for Sebastian no rubber band was used but they were quickly successful at finding the vessel.
Just before the big explosion, the hallways were filled with water. When the camera tracks the explosion through the hallways, there is no water present, not even vapor that should have been present if the heat generated from the explosion was enough to vaporise it that fast.
When Isabelle escapes the cage after biting Kensington on the hand, we see Caine walking out of the elevator and see that his arms are blocking his face through Kensington's goggles, the next shot, Caine's arms are by his side when falling down.
After his discovery, Caine notifies his team so early in the morning that the views from their windows are still as dark as night. But the shots of Caine driving to the lab were clearly filmed at mid-day.
Due to braking mechanisms and the fact that the elevator floor was at the same level as the lab floor, the fire would not have pushed the elevator upward. Instead it would have come up through the access panel that they opened, and possibly blown the top of the elevator off.
The pressurized tanks of flammable liquid that Linda uses to make a flamethrower are sitting unsecured in the lab. OSHA regulations require pressurized cylinders to be secured to prevent them from tipping over. The danger is that the top will get knocked off, and the tank will shoot around like a rocket. Any lab would have their tanks secured for this reason.
An injection into a vein will first reach the heart, then the lungs, after that return to the heart and finally distribute through the body. The sequence shown with the Gorilla and Cain returning from invisibility was anatomically incorrect.
Nitroglycerin cannot be simply mixed up in a matter of a minute or so. It requires careful and precise work (ideally under a fume hood), and very careful watching (the mixture has to be within a slim temperature range or it'll either not form nitro or explode prematurely). Also, nitroglycerin requires nitric acid in addition to the sulfuric we see him use.
The scene in which the gorilla is defibrillated has multiple errors. Defibrillation pads are supposed to be applied beforehand so that the animal can be defibrillated without delay. The skin should be shaved beforehand because shocks delivered through fur/hair can be ineffective. When Linda uses the external paddles, she yells "Clear" and then places the paddles. She should place the paddles first and then yell "Clear". Finally, the gorilla struggles against the restraints the entire time. Ventricular fibrillation produces unconsciousness within seconds, so the gorilla should be out cold.
The wire to a de-fib paddle is used as a constant power source for a powerful electromagnet. This isn't possible as the power source for a de-fib paddle is a capacitor which would only be able to emit a brief burst of charge.
The type of fire extinguishes used towards the end to spot Sebastian are type B, meaning they use carbon dioxide to take away the oxygen and release a heavy cold. This meant Sebastian (as well as the others nearby) would have passed out from lack of oxygen, and breathing in noxious gases. Much more of problem is when a flame thrower was used against him. His clothes and latex skin would not have protected from even one burst of flame like that. In fact, they would have fused with his skin and left full-thickness burns. If that did not kill him instantly, he would have been in way too much pain to do anything.
Since the viewing goggles used infrared radiation for seeing invisible objects, they could not see through a metal locker. However, the woman in the locker was leaning against, and hence warming, the door, and its her warmth that was shown.
While a defibrillator is of no use if a patient has truly flatlined, a patient in a "fine v-fib" rhythm can appear to have flatlined but still be revived with the paddles. Therefore, when in doubt, the Advanced Cardiac Life Support guidelines call for administering the shock, though it's not the treatment of choice.
Numerous problems inherent to the "invisible man" premise are completely ignored. Some examples: Since light passes through the retina Sebastian would be blind. The soles of his feet would be visible from the dirt picked up by walking barefoot. The food he eats becomes immediately invisible.
Caines colleagues find out about his rigging the thermal camera; they take out the altered circuit board. Caine later on looks at himself in the now restored camera, yet nobody confronts Caine about his manipulation, neither does he bring up the topic, even if that he now knows that they are on to him and they know that he knows.
When Sebastian is injecting himself with the serum, air bubbles are clearly visible in various shots. Anyone who knows how to administer an injection would try to get as much air as possible out of the liquid before injecting it.
After Sebastian (Kevin Bacon) has become invisible, the 3 main characters are walking him to the observation room where he sits down on the bed. After Linda (Elizabeth Shue) says the line "about time the shoe's on the other foot", she nudges him down onto the bed, turns and briefly looks directly into the camera, then obviously realizing her mistake, quickly looks away.
When Linda and Matthew lay on the bed and call Frank at the lab to check if Caine is still there, the end of the shot is slowed down in post production (possibly because it was too short for the intended edit), which is obvious from the blurred slow motion, especially of the receiver in the foreground.
Even if the lift had been able to fall unrestricted, it could not fall faster than Caine, as depicted. Its acceleration shouldn't be reduced by air resistance (especially as the fire below would increase pressure blow the lift) but even in a vacuum, the two objects (Caine and the lift) would always be falling at the same speed (as proved by Galileo at about the turn of the 17th century).
After being electrocuted and hit over the head with a crowbar, Sebastian is still very much alive and in good shape, considering. No mention is ever made that the invisibility serum also provides the subject with invulnerability and superhuman strength. A normal man would be killed if he were hit over the head with a crowbar. Also, lying on top of uninsulated steam pipes would have burned Caine, as would the escaping steam.