This thread is inspired by randomly starting to read Bill Bryson's 'A Walk in the Woods' which has been sitting on my shelf for well over a decade. I've only read the first couple of chapters - the first includes many horrible and scary things that can happen to walkers on the Appalachian trail, the second focuses in particular on bear attacks. Quite why he didn't say 'sod this, I'll go back to the UK and do the Coast to Coast' eludes me.
I think by the end of the book I shall have an increased gratitude for living and walking mainly in the United Kingdom where the worst that can happen is... what? Here's all I can think of. I expect someone will top mine but please do enter yours even if it really was exceptionally tame. 
Adder encounter - DH pee'd on one behind a tree. It slithered off. Not very perilous at all. Well, the adder might beg to differ.
Lone bullock - chased DH and I through some woods where it shouldn't have been. We think it was lost and discombobulated. Quite perilous, it was big and faster than us, fortunately it didn't follow us up a steep slope.