Charlie's burning skin and practically boiling blood are an effective defense mechanism, that's one thing he can say about them. As soon as the too-hot blood reaches his mouth, he yanks back, scalded, his brain beginning to snap back to normal.

Or at least normal enough, though he's still feeling altered from the effect of the blood, to be horrified by just how pale and close to passing out Charlie looks. This is why he didn't want to do this. This is why it was a bad idea.

And yet... he finally feels satisfied, for the first time in days.