When they come a knocking it's quite simple you say,
"Oh hello are you the Morons or the other lot ? Never mind, the agency did tell you to bring old clothes & aprons didn't they, these sacrificial slaughters can get pretty messy & you wouldn't believe the problems we have trying to find virgins round here so we usually have to make do with one of the old dears from the home instead."
Funny they don't want to hang about.