The missing sock mystery

Bought new socks
Emptied washing machine after their first wash - only one there.
Felt all round the drum nooks and crannies - no trace.
Checked not escaped when transporting from basket to machine -no trace.
Checked remaining washing remaining - no trace.
Did a ' white wash' - out popped the sock!
How does that happen?

Gave Green Gym a miss as still not feeling 100% and weather wet and miserable, but haircut this afternoon brightened things up a bit and think I might manage yoga tomorrow.