Continuity mistake: When we see Melvin's bedroom, when Simon is looking for the dog, the shelf above his bed is half filled with books and bottles of water. By the end of the phonecall with Carol, the shelf is completely filled. (01:58:15 - 02:01:20)
Continuity mistake: Simon has a rack of pool balls on his coffee table. When Melvin is telling Simon about the bacon, the 2 ball (solid blue) is near the telephone. In the next shot, the dog jumps up to get the bacon and now the 3 ball (solid red) is near the phone. (01:01:20)
Answer: It has everything to do with his mental illness. His OCD condition has kept him isolated with anti-social tendencies. He just finds it difficult to directly interact with people.
raywest