At the start and end of Zazen, it is customary to bow. I always thought this bowing was to the buddha, but when I learned more about Buddhism realized that the Buddha himself advised not to admire the Buddha too much, and that we are all buddhas.
So who are we bowing to? In a hall of practitioners, you’d bow to your neighbor on the left and right. I’ve never practiced in such a hall, but when I do zazen solo, I bow in order to give gratitude. To everything and everyone.
It sounds fluffy, but it’s more centering than it appears to be at first. When I bow, in trying to think about what I’m grateful for, I end up cycling through a list of people, then large groups of people, until I realize that, really, I’m grateful for everyone and every piece of the puzzle. It’s too overwhelming a feeling to think about for too long. A bow is just long enough.
You could also think of it was “boh-ing” – like the type of bow you put on a present. We start and end with a “bow” to tie the experience up in spiritual gift wrap.