That is really interesting to me. I admittedly haven't played with it in a while but on previous Android phones I've had basically any patch of skin would register and work okay with the sensor. I know because I used to rock climb a lot which tears up fingerprints so I would register things like the backside of my index finger so I could unlock the phone while it sits on a table. It was definitely finickier than a proper fingerprint but preferable to retraining it every couple of days.
