The end of a snapped off branch hit the front of my helmet.
Looking at how far it went into the helmet I'm glad it wasn't 1cm to either side or it would have been pretty serious
It did virtually stop me in my tracks and my neck is pretty stiff this morning.
You can see how much force there was - it nearly ripped the straps out of the shell at the front;
The velcro strap on my lamp snapped as well.
Weird thing is I've ridden that bit of singletrack dozens of times and never even noticed this branch as being a 'hazard'. When we looked at it afterwards it was an accident waiting to happen - very sharp, at head height when on a bike, facing up the trail so you only saw it end on. Snapped it off the tree now - it was a dead branch anyway.
Oh well, could have been a *lot* worse.