One of my early mentors worked on it. They mentioned the pulsation for the sleep indicator was modeled not just on the human respiratory rate, but specifically that of a sleeping adult. It came up when we were playing around with on/off dimming curves for a room based video conferencing product and discussing physical analogies we could model a curve on. Fun afternoon exploration, but in the end we just stuck with ease-in/out. I miss when you didn’t need to overly justify taking an afternoon detour to explore whether something could be improved.