When I move Butter to his outside explorium, he hisses and puffs up and opens his mouth at me...hasn't bitten yet, but then I keep my hands away from his mouth!!! Once I get him outside, he calms down a bit, until he sees the explorium, and then wants to jump in.
Taking him back inside garners the same response, in reverse.
I use the few moments I'm holding him to take a good look at him, check for any changes in his body, take a good look in his gaping mouth .....