Why is it that some people "have a thing" for gross bodily secretions (and other stuff)

Subcutaneous cysts – watching someone pop one of those suckers; peeling off what was once sunburned skin (Goldmember); checking out someone else’s tonsil stone removal online, popping someone else’s blackhead; why do people enjoy seeing all of that?

My Dad had a huge Subcutaneous cyst on his back; we were camping, and my Aunt (who is a banker and a proper lady) nearly tripped over her own damn feet to have a look, as my sister (who is an R.N.) was ready to incise the cyst and squeeeze!