It's a big part of how Ponyville was founded, believe it or not.

[Well, what else to do on a rainy day than tell stories? She shifts a little to get more comfortable before she starts into it.]

Well, there's five days leadin' up ta the harvest. Each day, somethin' else happens that's a sign the zap apples're comin' in. It all starts off when the timber wolves start howlin' out in the forest... that's how ya know the zap apples ain't far off.