You don’t see them hop, you see them before the bounce, and if you are fast enough, you can see them once they land. But when they jump it’s completely different. Each parasitic intruder is moving so fast they can’t be seen. It means for that fraction of a second between jump and land, they are everywhere at once. There is no space that is not filled completely with fleas. When you can’t see them it means they are in motion, looming closer to us with each unfurling of bristled legs to pop into the every-space and then back.