Leaves fall all the time this time of year and mostly Pepper ignores them. But one day, while out on a walk, the leaves caused him concern. In a fictional scene, he would bark at each leaf, trying to bite it out of the air. In real life, he was merely distracted by them.
A leaf would fall and the sound of it hitting the sidewalk would make him turn towards it. As more and more leaves fell, he started to get scared of them. If a leaf fell in front of him, he would turn and go the other way. Enough leaves kept blocking his path that he starting running home.