A couple of years back, I was riding through Bruce Ridge, and there's a section just before the FoBR Pub Run that's pretty tight and scrubby, but lots of fun to ride though. This day, I misjudged a gap between trees and hit my shoulder against one of them, nothing too hard or anything though.
A moment later, out of the corner of my eye I see what looks like a weird growth on my shoulder, it almost looked like the area had erupted out violently. So I hit the brakes while wondering what the hell I've done to myself, and why I'm not in agony, stop...and realise that I'd hit a big glob of sap on the tree trunk, which had come off and stuck to my shoulder! It was a pretty big relief to realise I hadn't destroyed myself!