I can understand the harmonica - that's both sucked and blown so yes, bodily fluids.. eurgh!

I'm reliably informed that what comes out of the end of whistles and flutes is water, rather than dribble (but there are one or two 'moist' players that I would avoid sharing with), so I have no problem lending out any of my instruments... but then as I play percussion or recorders, no-one ever wants to borrow them anyway!

LTS