Given scene/plot descriptions from movies or TV shows, and given a specific question about the scene, summarize the question into a title

In season 3 of Game of Thrones, Daenerys Targaryen buys Unsullied in exchange for one of her dragons. After turning over the dragon's leash, she is handed a decorated whip as a symbol of ownership. She then orders the Unsullied to "Slay the masters,... slay every man who holds a whip..." The Unsullied stand motionless as Kraznys mo Nakloz, the seller, screams back at them to kill Daenerys. She then commands the dragon to incinerate Kraznys, after which the Unsullied sack the city. Is the delay before the initial attack simply for cinematic effect? Or did Kraznys train the warriors with a fail-safe, to refuse any order to kill him, which required him to be dispatched first? If the whip gives command, how can Daenerys order them to kill other whip holders? Couldn't one of them countermand the order? Or are they motivated by revenge against their former masters?
How do the Unsullied prioritize their orders?