Continuity mistake: Right before Paul says grace, Dr. Lecter checks the time on the grandfather clock. We see a long shot, and the hand's on about 46 minutes. Then there is a closeup of the clock moving past 50 minutes after the hour. When it cuts back to the table, the clock is immediately back to 46. (01:56:19)
Continuity mistake: During the dinner when Clarice tries to stab Hannibal, his hand goes from on her wrist in one shot to the back of her head in the next. (01:58:20)
Continuity mistake: In the flashback seen where Dr. Lecter suggests to Mason Verger peel off his own face, Dr.Lecter picks up the broken mirror piece with a navy or black cloth. Then in the next scene, when he hands it to Mason, there is no cloth. Then, when Mason starts to scrape away at his face, the cloth reappears in Mason's hand.
Continuity mistake: When Pazzi sits down during Hannibal's presentation, Hannibal puts his hand on his shoulder. It is suddenly in a slightly different place in the closer shot without there being time to move it. It's very slight but still noticeable.
Continuity mistake: During the brains-for-dinner scene, Clarice sneaks her knife under the table to use against Lecter. A few lines of dialogue and camera angles later, the knife is back on the table, and Clarice sneaks it under the table - again.
Continuity mistake: When Lecter is being wheeled in to talk to Mason Verger, he has blood on his face from the beating he got in the van. When he talks to Verger, the blood is gone.
Continuity mistake: In the kitchen after the brain dinner party, Hannibal throws a towel on top of Paul's open skull. When Hannibal throws Starling against the fridge and she fights back, Paul is sitting with his skull back on.
Continuity mistake: In Italy, when Hannibal grabs the glass with a napkin around, the way the napkin is folded changes between shots.
Continuity mistake: In the pig pen, when Clarice is shot down, her gun changes positions between shots.
Continuity mistake: In the scene where Hannibal picks up a meat cleaver to chop off the handcuffs attaching him to Starling; in one shot it is covered with chopped herbs, in the next it is clean.
Continuity mistake: In the scene where Clarice wakes up in Krendler's house heavily drugged, she looks at her things on the chest outside of the room. Her denim jacket is there. However, we see her take this off and leave it in her car when she decides to go in to the Verger barn.
Continuity mistake: In the scene where Clarice visits Barney, in each shot the fan switches from off to on and back, both before and after Barney turns it on.
Continuity mistake: When the pigs come out and Hannibal holds Clarice, her left arm is either on her tummy or hanging loose by her side, depending on the shot.
Continuity mistake: At the market, when a black thug is crushed between two cars, stones on the white car's roof disappear in the wide angles, but reappear in the close-ups.
Continuity mistake: When the baddies' car runs Bolton over, he smashes the windshield, but the damage and blood disappear in the next shot.
Continuity mistake: The first time we see Clarice she approaches a car. A bang of hair suddenly appears over her forehead between shots.
Continuity mistake: When the movie begins Barney shows the pink box and places his hand on the string attaching its lid. A frame later, the hand is away but the knot is magically untied.
Continuity mistake: The letter to Clarice is folded twice when she opens it, yet Hannibal is shown folding it once. (It was not a second fold because we see two edges touch, not a fold and one edge.)
Answer: In the book it says that Clarice had caught Buffalo Bill before he could. It said also that is why he hated her early in the book.