I work at a riding stable, and the horse I ride (I also have lessons twice a week, which was how I came to work there) Pepe
, is petrified of Gum tree branches breaking or snapping. I will be working him in an arena, and he will literally stop, ears pricked WATCH the tree snap, listen to it, snort, and stand there for about 10 seconds... then flip out (hes jumped and twisted.. bolted, bucked). He's such a goof, I love him.
His reaction is pretty much "Oooh the trees breaking, wow that was loud..hmmm what to do, what to do... OH $h1t.