I don’t know about scariest but it is up there. Was trampling around a jungle like a moron in South East Asia when a lizard the size of a small dog just crossed my path. Something about it gave me the impression (probably wrong but fear is personal not always rational) that if I had been in its way it would have bitten me, I would die of sepsis in a few days, and that lizard would have forgotten about me 3 seconds after dooming me.

There is something about facing a danger with no intelligence behind it.