Catherine claims the mother of the victim lied because she moved her eyes to the left when answering her question. The theory is in fact that a person would be telling the truth because they are accessing auditory/visually remembered event. This is correctly explained in The Negotiator.
When Brown collects the "ice" at the crime scene, he places it in a sealed container with a screw on top. Later the "ice" is found to be missing, and he realizes that it was dry ice. If it was dry ice, the container should have exploded as the gas pressure inside increased.