Well, I didn't realise initially that each size of snake totem would open a corresponding level of the pyramid. I was just max sizing it each time before placing it on the plinth.
That reminds me, I encountered a bit of a bug in the middle section of the pyramid. I had a one of the stone snakes clip through another briefly (collision checks) but then after that the ball did not connect with the mouth of the final snake properly.
I recorded this in a YouTube video I made of my play through.
Jump to 15m 25s to see it.