A key difference between Blackjack and Spanish 21 is that all 10s are removed from the deck in Spanish 21. A Blackjack occurs when the first two cards that are dealt equal 21 a combination of a face card (Jack, Queen, or King) and an Ace (which can have a value of 1 or 11, depending on your hand).
But the idea is that when someone shouts "monkey" they are not really asking for the dealer to bust, they are asking for the next card to be a "10" card which may well bust the dealer if he has a stiff of course.