Cerebral,
Renwar told you right; the "Go, shorty..." is part of the intro.
On "In Da Club," the chorus is the hook.
In fact, that's USUALLY (not always, but usually) the case in modern music.
The hook is not the part that gets stuck in an individual's head; it's the part intended to stick in the heads of the most of the listeners.
The hook is almost without exception a part of the song that is repeated several times during the course of a song. One of the primary purposes of the repetition is to drive that part into the listener's head.
All the talking Timbaland does in the background of most of the songs he produces might very well be the part that sticks out most to an individual listener. But that doesn't make it the hook.
Of the explanations given, geedubbee's was the most accurate.