blackjack dealers

In Blackjack how the dealer if you have a bust or not?
I wondered how a blackjack dealer know if you have a bust or not because I do not think they see that you are right? ♠ ♣ ♥ ♦
I do not play but I think his two cards face up while the dealer has a card, but I may be wrong.
Clark Griswald vs Marty the Blackjack Dealer (National Lampoon’s Vegas Vacation)