The idea is to yell it loud enough so the deck of cards can hear you and produce a pikcha (picture) card so you will finish on 21.
Sometimes can be yelled out when you have 10, 9 or even 8 and you desperately need a picture card.
* You have a 5 and a 6, the dealer points to your cards *
* You take some chips and match your current bet *
Dealer: "doubling down, on 11, one card only..."
* Dealer reaches for a card *
You: "PIKKKK-CHAAAAAAAAAA!!!!" (pikcha)
* The card is a 2 *
You: "for fucks sake"
Dealer: "13, play or forfeit?"