Character mistake: After Pookie is killed (with his eyes open) and the bomb is strapped to him, he blinks his eyes.
Character mistake: When Garrison is leaving the house to question Clay Shaw on Easter Sunday, his wife is complaining about his working on the Sunday, and at one point calls Garrison 'Clay'.
Character mistake: Buffalo Bill's revolver is a double action, meaning did not need to cock his gun before firing it (you only need to do so with single-action revolvers. Cocking a double-action just makes the next trigger pull easier.) He could've just shot Starling. His stupidity got him killed.
Character mistake: When Dolph is looking at the logo for the Red Dragon brewery, he says, "That arrogant scumbag mother fucker. He put the yakuza iron claw right on the logo." But, the iron claw is not the logo of the yakuza. It's the logo of the specific syndicate run by some members of the yakuza, as Dolph stated after ripping open the shirt of that guy in the interrogation room. So, he just wrongly stated what the logo really belonged to.
Character mistake: Whoever wrote the "homicide" memo on the captain's corkboard spelled "homicide" wrong.
Character mistake: Gail is interviewing Nick on the steps with a tape recorder. You can tell she's holding down the wrong buttons. The record button is in the up position. She's not recording anything.