Factual error: After Detective Mike looked at Shane's body, the camera shifted to an aerial view of the city, which showed Fall foliage but it was after Christmas, when the trees in Chicago would have already shed their leaves. (00:40:50)
Factual error: Chucky murders his first (human) victim as he was taking down the Christmas lights, making him fall in the watermelon patch in front of his house. Shane must have an uncanny green thumb, to be able to have fully grown watermelons in winter.
Answer: According to IMDb, the supervisor is basically chewing him out for being lazy and sleeping on the job, and then fires him.
TedStixon