Question: Why did Erle try to kill himself?
Question: How can Michael recognize Laurie as his younger sister since he wouldn't have seen her since she was only two years old?
Answer: There is a scene where Laurie dreams about meeting Michael as a young teen. It's unknown whether this is an actual memory of real events, but since nothing indicates otherwise, we could assume the he saw her at an older age when she looked closer to her 17-year-old self.
Question: It is implied that Satan and the forces of evil are always watching out for Damien so that when anybody gets anywhere near to hurting him they invariably meet a very sticky end. So how is it that, at the end of the film, Kate Reynolds is able to stab Damien to death with such apparent ease when all previous efforts to kill him have failed so dismally?
Answer: Damien states at one point that as the birth of the Nazarene gets closer, his strength fades accordingly. Presumably this also applies to any forces assisting him.
Question: Matty introduces her friend as Mary Ann, but in the year book, the friend is actually Matty Tyler, and she is actually Mary Ann. Were both girls in on the scam? (00:31:22)
Answer: I noticed the problem of the introduction, also. It seemed like a major plot hole to me. There wasn't any material in the movie to support blackmail, etc by the real Matty. I hadn't thought of her possibly being in on the scam. If not, why wouldn't the real Matty have immediately blanched when hearing herself be introduced with the wrong name? So far, I agree with the OP's suggestion.
The real Maddy was at the house when Ned arrived. Presumably, she had already discovered what "Fake Maddy" was up to. It looked like Fake Maddy (Turner) gave the real Maddy a check, presumably a payoff to keep quiet. The real Maddy may or may not have known exactly what Fake Maddy was planning, but went along with being introduced as "Mary Ann." Also, the movie deliberately leaves details vague because it is a big plot twist at the end when Ned, and the audience, learns that Fake Maddy is really Mary Ann.
Answer: It appears that the real Matty Tyler was not initially in on the plan. It's confusing, and there're many plot holes, but it seems the fake "Matty" (Kathleen Turner) intended for the real Matty to eventually discover that her identity was being used (by Turner). The real Matty was then apparently blackmailing fake Matty to keep quiet. It appears that fake Matty intended to lure and then murder the real Matty, framing Ned Racine for her murder, as well as Edmund's. The real Matty's body was identified as being Edmond's wife through her dental records. Fake Matty probably intended for Ned to be killed in the explosion.
Question: What did Dr. Hirsch mean when he said to Alex how he witnessed "some form of mass neurosis in East Proctor"?
Question: Evil tells of his assistants, "tell me about computers". And he later says, "show me subscriber trunk dialing". Why does such a powerful entity have an interest in technology? (01:30:45 - 01:31:35)
Answer: Remember his whole speech about technology being his version of the universe, while the Supreme Being concentrated on nature?
Question: What was that first body in the woods that looked like Muffin? It couldn't have been Muffin because she shows up at the end right?
Answer: It never really says what the body is, but I'd assume it were a rabbit or some other small woodland creature. It can't be Muffin because, like you said, Muffin appears later on.
Question: How did Snake lose his eye?
Chosen answer: During a mission known as the "Leningrad Ruse." He and his flight squadron were sent unknowingly on a suicide mission. During it, his goggles cracked and let in a poisonous gas, paralyzing his iris. He has to wear the patch because his eye can't focus against bright light, causing pain. This is mentioned in the novelization.
Question: It appears that the boomerang would have had to spin in the opposite direction to kill the blonde guy the way it did. Am I looking at this the right way or is my limited knowledge of aerodynamics totally backwards?
Chosen answer: The filmmakers obviously didn't research the intricate logistics of aerodynamics of how a boomerang is thrown. It simply looked cool leaving the kid's hand and killing the blonde guy the way it did.
Question: What happens to Harold? We go from him killing a classmate to present times where he works as an intern in a hospital. Surely he'd have been in juvenile hall then prison or in a psych ward.
Answer: It is never explained but the implication is that he has somehow escaped justice for his earlier crime and is using a new identity.
Question: Is this the only Bond film that features any references to Tracy Bond (other than the given "On Her Majesty's...")?
Answer: It's mentioned he was married in The Spy Who Loved Me and Licence to Kill.
Answer: It is also vaguely alluded to in The World is Not Enough. When Electra asks Bond, "tell me, Mr. Bond, ha- have you ever lost a loved one." And it's written all over his face, so to speak.
Answer: He hated the way they were living. Acting human, hiding who they truly were, integrating into "normal" society. He wanted to be wild and free. When they were feared and worshiped.