Slave Owner's Payment Method

Alright, listen up, you big dummy. You know how people buy stuff with a credit card, right? There's a famous one called 'Master Card'. Now, get this: in the old, bad times, someone who owned slaves was called a 'master'. So, the joke is a really dark play on words because a 'master' would use a 'Master Card' to buy slaves. It's a pun, you dolt! Because 'master' means two different things here. Now go on, you're welcome.