Three times during the night/early morning I heard Theo making the dreaded urping up noise. All three times I scrambled out of bed to try to move him so he wouldn't throw up on the carpet. Each time I'd approach him though, he'd run away.
The first two times he didn't urp anything up. This led to a theory that a cat can't throw up if they are running. I was about to make a note of that until the third incident. This time Theo did throw up while he was running leaving a trail down the hallway. D'oh!