Continuity mistake: After Brian finds the note Alf left, we see William put the note under the microscope to inspect the tear drops. When William says "I'm going to go find him," he stands up and we see him leave the note on the microscope. When the camera cuts to William walking through the door, he all of a sudden has the note in his hand that was left on the microscope. (00:12:55 - 00:13:35)