I killed a Pi Zero by forgetting how the GPIO pins are numbered.
So, on the headerless Pi there is a hint about which is pin zero (lower board); but not on the upper board. Dumb me, I attached what I thought were GPIO21 and GND (physical numbers 39 & 38) to a sensor. Instead I connected pins 0 and 1 (+3.3v & 5v). Good by Pi Zero.