The bank has to buy the cows right away? I thought when the redditor buys the call someone else, let's say Bob, sells the call. If Bob already owns 100 cows (covered calls), then no one will be forced to buy cows ever. If Bob doesn't own 100 cows (naked calls), Bob will have to buy 100 cows at the end of the month if the call is in the money, not right away.