GOX

You gave your two cows to a rancher
Someone comes in to steal 1, 2, or none of the cows (you don't know)
The rancher blames the thief for stealing his cows, but says you still have two cows
You go retrieve your cows, and find an empty field. The rancher also moved.
You call the rancher, who says your cows are still there
Someone is standing outside selling his cow for two of your "cows".