About a half hour ago Stan came out of his hide and I suddenly heard a sound that kind of sounded like when a cat is hacking up hairballs and I ran over there I heard it a time or two more and then Stan hissed (which I've never seen him do before) and "yawned" and then went on as business as usual.

I checked his tank for anything strange and everything was as usual. I picked him up to take a look at him and he was acting fine. I even checked for the symptoms of RI (even though he wasn't whistling) and there was no mucus or anything and he isn't stargazing.

What do you think was happening?