Creeper starts flashing animation when bouncing on slime block

I built a large (5x5) platform out of slime blocks, built a tower (about 15 tall) next to it, spawned a creeper on top, and pushed the creeper off so he'd land on the slime block platform. While he was bouncing on the platform he randomly started flashing like he was going to explode (without hissing audio) and then stopped.