Stock market tips and wine choice may be two things you shouldn’t ask your waiter about.

When enjoying a glass of wine, you may want to consider its cost when compared to the cost of a whole bottle.

Restaurants are naturally going to try to recoup the cost of the wine and make a profit. Zagat reports that at most restaurants, the price of a glass of wine is what they paid for the entire bottle wholesale.

There’s more: You wouldn’t eat someone else’s leftovers when you go out for a meal. Then why would you want to drink their leftover bottle of wine? That’s exactly what can happen, Zagat reports. Especially if someone else orders a bottle of wine and then decides that they don’t like it, some restaurants will serve it by the glass.