Many dogs in the town have gone missing as part of the plot, and the missing dogs are discussed in conversation. A dog skull and collar are found on the beach. No dogs are harmed on screen.
Newspaper shows a lot of pictures of pet dogs who've gone missing. You see a dog skull and a collar washed up on the beach. Mention later of a pet pigeon being killed with a phonebook.
Doesn't quite get to that point, but there is intent. Later on the main character's mother is stated to have electrocuted herself on a toy in the arcade (on purpose, it seems to be an electric eel game) but it malfunctioned and actually electrocuted her to death. I don't think this was on purpose but I figured I would add this here just in case.
Autism isn't mentioned but the main character is seen to be a little slow (possibly with learning difficulties) and is abused verbally by his girlfriend and older brother for not understanding things.