Continuity mistake: When Laurie's mom is struggling to get to the phone after Michael stabs her, she reaches for it, knocking it off the hook. When Sheriff Brackett calls later on, the answering machine picks up.
Continuity mistake: Laurie drops the items in the mail slot twice at the Myers' house. (00:58:30)
Continuity mistake: In the beginning, after Michael kills his sisters boyfriend, he puts the mask on with bloody hands yet he gets no blood on the mask.
Continuity mistake: When Laurie stops at the Myers house she has no backpack. She does in the next scene.
Continuity mistake: When Grizzly the truck driver stops at the truck stop, the attendant opens the hood and gets the hose twice.
Continuity mistake: Laurie's hair changes from curly to straight frequently in the Myers' house.
Continuity mistake: When Michael Myers busts into the bathroom stall occupied by the truck driver, the glass on the framed advertisements on the opposite side of the stall is broken and we hear glass hitting the floor. When Myers leaves the stall, the glass in the frame is still intact.
Continuity mistake: Near the film's end, Myers crushes Dr. Loomis' skull with blood protruding from several parts of his face. In the following shot of him being dragged into the house dead, his face and head are perfectly fine.
Continuity mistake: When Michael beats the kid in a park with a stick, the attack only lasts a minute yet the new blood on the kids face is dried up, presumably from earlier takes. The dry blood effect is seen in more scenes throughout the movie.
Continuity mistake: 10-year-old Michael has just returned home from trick-or-treating and is eating candy in the kitchen. The black handle of his pumpkin basket is raised in close-up shots while down in other shots.
Continuity mistake: Michael goes to his last meeting with Loomis bare faced and wearing a robe. Then he's sitting there not wearing the robe and wearing a mask.
Continuity mistake: Michael runs at Laurie and they both land on the ground. All the way down, Michael is on top of Laurie. Next shot shows Laurie on top of Michael. (01:53:45)
Answer: He was hoping that Laurie would realise that she's really his sister. However, because Laurie was just a baby and raised by another family, she had no idea why Michael was showing her the picture or what it had to do with her.