When Warrick makes a tracing of the knife, he does so rather sloppily. The two lines he makes do not meet each other, and the top one extends past the knife. Yet, when they measure the wound castings for the "blunt object", the tracing is perfectly done, with one solid line going from top to bottom.
Catherine says that when you point a finger at something, the other four are pointing back at you. This phrase is usually expressed as "when you point the finger at someone else, the other THREE are pointing back at yourself." Many philosophies embrace this karmic platitude and usually express it as "whatever you do, whether good or bad, will come back on you threefold," or something similar. Physiologically, it's impossible to have one finger pointing at something and four fingers pointing back at yourself, unless you manage to make the pointing finger the thumb. Most people point with their index fingers, and, in fact, many anatomists do not even consider the thumb to be a finger.
When it's shown how Jessica got stabbed, she clutches the left side of her abdomen, indicating she got stabbed there. When doing the recreation while trying to figure out how her blood got on the other victim, Sara clutches her right side. She should know which side the victim was stabbed on.