Character mistake: Dissecting the chrysalis, Dr. Roden says that "Somebody grew this guy. Fed him honey and nightshade." Nightshade is indeed one of the typical plants eaten by the Death's head moth, but since "he" is only a pupa, would have not eaten honey, which is something only the adult specimen eats. (00:48:50)
Character mistake: Clarice was given clear, explicit instructions by Crawford before going to the asylum to see Lecter, including: do not touch the glass; do not approach the glass; tell him nothing personal; do not accept anything from him. Barney also gave the specific rules to Clarice when she got there (e.g, "you don't get near the glass"; use the food tray carrier to give him papers), and informed her he would be watching her on video. An FBI Agent TRAINEE is under close scrutiny and failure to meet the high standards and/or rigorous training can/will result in dismissal from the academy; a student must follow the rules and demonstrate she has what it takes to graduate and is suitable to become a member of the FBI. Given the high standards and relative difficulty in securing a position with the FBI, a trainee would not blatantly break the rules or virtually disregard the direct orders of a supervisor like Clarice did - especially during the very first assignment. The end does not justify the means.
Character mistake: When the scientists cut open the cocoon found in the throat of a murder victim, they are not wearing gloves even though Clarice specifically states that it was found behind the soft palate of a murder victim. (00:48:00)