I was at my parents' house last night, and Carolyn was at hers, three doors away. She phoned me to warn me that her children and their cousin were heading my way, trick or treating, so I had better answer the door rather than pretending nobody was in.
She phoned me again today to say thanks, and explained how, after they had amassed a decent haul of sweets, the children had gone back to grandma's and sorted them into two piles: sweets they liked, and sweets they didn't. They then gave the second pile to grandma and got her to palm them off on other trick or treaters.
I wonder how many sweets ended up back with their original owners.