stretching their little proboscides up and flop around like a slow version of those inflatable airdancers used to advertise car dealerships

Thank you for this vivid description. Yet another reason for me to tuck my pants into my socks.

Once I was in some rock pool, wearing some old converse with holes in them because of the rocks.

I must have stepped in a nest or something, because when I took the shoes off I had like 50 tiny (like rice-sized) leeches on one of my feet.

Thankfully they came off easily.