Legless bikers

I pride myself on having a fairly high pain threshold but this guy just takes the biscuit! Reuters reports that:

a Japanese biker failed to notice his leg had been severed below the knee when he hit a safety barrier, and rode on for more than a mile, leaving a friend to pick up the missing limb.

The man and his leg were taken to a hospital, but the limb had been crushed in the collision.

I mean, how do you NOT notice something like that?