Leviticus 9:13

‘And they delivered the burnt-offering to him, piece by piece, and the head, and he burnt them on the altar.'

Then his sons handed him ‘piece by piece' the parts of the sacrifice, including the head. It is clear that the task of skinning it and cutting it up had been left to them due to the necessities of the situation (Aaron could not do two things at once). Thus as each cut off a part they handed it to Aaron. This accurate and unusual description again confirms that we are reading the evidence of an eye-witness. And as he received each piece he laid it on the flames of the altar.