Last night, I was playing with our two cats for about 30 minutes using a toy mouse tied to a plastic stick (they LOVE that toy). They were playing pretty hard, and after about 30 minutes, one of them was panting very hard with her mouth open and tongue hanging out. She looked like a dog! It freaked out the other cat. I've never seen a cat breathe that hard before. When that started, I put the toy away and let them calm down. Is that normal?