Breathe in. Breathe out. pOnd is a one-switch game like no other. Your one-switch control is linked to inhaling (hold) and exhaling (release). It does require accurate timing, and some will find a latching switch helps. Later, JoyToKey's auto-fire could help those needing assistance in rapid-taps, without wishing to give too much away.
Many thanks to Gavin Philips for the tip-off.