I always felt it was from David's perspective of what is unimaginable to any human, and the scene is just his feeble mind attempting to make sense of something

I always felt it was from David's perspective of what is unimaginable to any human, and the scene is just his feeble mind attempting to make sense of something that his body can't. Much in the same way he experiences himself grow old and be reborn; he's being shown something he can't comprehend in a way that makes it easier for him to experience and understand. It's not meant to really be literal. At least that's my take, I could be wrong!