Really? really? The trouble is, once you explain a joke, it's usually not funny anymore but here goes - in a light hearted way I just though that explaining away the presence of morphine in a horse by saying the food was contaminated, seemed a bit of a stretch!! I was just amused by it as an unlikely scenario. I then said pull the other three because it was about horses and horses have four legs and with humans we say pull the other one because we have two legs. There I told you it wouldn't be funny after I explained it but thanks Iam for getting it.
I still think the funniest joke I ever saw was a cartoon of two hippopotami wallowing in the mud-one says to the other '.I keep thinking its Tuesday'
( just fell off my deck chair remembering it)