Whenever PIKACHU comes across something new, it blasts it with a jolt of electricity. If you come across a blackened berry, it's evidence that this POKéMON mistook the intensity of its charge.
Sapphire:
This POKéMON has electricity-storing pouches on its cheeks. These appear to become electrically charged during the night while PIKACHU sleeps. It occasionally discharges electricity when it is dozy after waking up.
Fire Red:
It has small electric sacs on both its cheeks. If threatened, it looses electric charges from the sacs.
Leaf Green:
When several of these POKéMON gather, their electricity can build and cause lightning storms.