Here's a funny trick to mess with them. This appears to be taken in some sort of grocery, as I see canned goods. Grab some ground hamburger or some other meat product from the meat counter and slide it under the bottom shelf where noone can see it. Wait three weeks.
Hell, wouldn't have to be three weeks, whenever I've gotten something from the butcher or deli counters in that store (Sainsbury's East Filton, should any of the fuckers in question go a-Googling) I've been ill. Sure, most of the time it's probably been coincidence, Christ knows I came down with every baby bug possible last year, but all the same. But when you have to go to hospital with a forty-degree fever that your wife or baby doesn't catch, after eating something from their deli range, you have to wonder.