Plot hole: We see Michael wearing the mask throughout the day, from morning at the Myers House, to mid-day outside Laurie's school, to afternoon when Tommy is leaving school, yet when Laurie and Annie see the sheriff in front of the hardware store on the way to their babysitting jobs (presumably in late afternoon or early evening), the store's alarm is still ringing and the sheriff mentions that one of the items stolen was a Halloween mask.
Plot hole: At the beginning when the SWAT team breaks through the door in the basement and all the zombies escape they don't attack the SWAT team they just run up the stairs.
