A vampire enters a bar.
- I want a little glass of blood, please.
- Do you have a preference ? the bartender asks.
- No, no, no, as long as it's fresh.
Five minutes later a second vampire comes in turn.
- I would like a small glass of blood, but of group B, please.
And the delighted bartender says:
- Hum, um, I see that you are a connoisseur ...