[yosamino]

> Of course, someone might be able to clone your head shape.

This is from 2005:

> Police in Malaysia are hunting for members of a violent gang who chopped off a car owner's finger to get round the vehicle's hi-tech security system.

http://news.bbc.co.uk/2/hi/asia-pacific/4396831.stm

I guess this is a question of threat model. I hope nobody would want to chop of my head just to unlock my iphone. But this always reminds me of the scene in "Demolition Man" where Wesley Snipes spoons out someone's eyeball to open the biometrically locked door of his prison.