So are we all agreed that sawing....

[Adny]

CowardlyDog is half right.

It's hot in the brazen bull. Humans are 70%-ish water. Water turns to steam, the air would be unbreathable, then the unlucky son-of-a-gun would pass out from not being able to breathe. They wouldn't be conscious for their death, but the time they were awake wouldn't exactly pleasant either.*

*=This is how it was explained in "1000 Ways to Die", since everyone else seems to be pulling information from it.