^^ I don't remember that. Did he not even try? I would think in a situation like that, he would regenerate repeatedly until he ran out.
Can he do it again so soon, especially now that he's older?
Seriously though, I always thought some time had to pass while the regeneration energy built back up or something. The first regeneration I ever saw was 9 to 10, and the process seemed to continue throughout the whole adventure. Isn't the reason he can re-grow a hand stated to be because he's not quite done with the cycle?