What does “cramming” mean? Can I use this word to human as well?
"Cramming" in this case refers to cats forcing themselves to fit into a tiny space. In general, to "cram" means to shove things together or fill an empty space until it is full and can no longer fit any more inside. This verb can be used to describe anything that occupies a space, and so it can be used for humans as well. Ex: The people are cramming into the bus. Ex: The sink is crammed with dishes.