Executive Meddling: There were a few instances where the crew had to get creative in order to make the murders palatable for Network television. Bryan Fuller told an amusing anecdote about the "angels" from Coquilles:
"NBC said, 'we cannot show that shot' - which was this great, kind of cinematic shot - and I said, 'Why? Because of the exposed spine and muscle tissue and ribs and flayed skin?' and they were, like, 'No, we see their butt cracks.' And I said, 'What if we filled the butt cracks with blood so you didn't see the crack?' and they said 'Okay!'"
Fake American: Hugh Dancy, who plays Will, is actually British. In fact, only Jack and Beverly are genuine Americans. The rest are English or Canadian, with Danish Mads Mikkelsen playing ambiguously-European Hannibal Lecter.
Missing Episode: The fourth episode was pulled from the schedule, and the character-important segments were later adapted into a webseries designed to fill in the gaps. But then iTunes subverted this by putting up the uncut episode.
Eddie Izzard, best known for his stand up comedy and cross-dressing, plays a terrifying Dr. Gideon.
What Might Have Been: David Tennant tried out for the part of Lecter. He didn't get it (obviously), but Bryan Fuller was so impressed by his audition that he expressed the desire to write him a part as a psychopathic serial killer later in the series.
Apparently, Fuller initially considered Lee Pace as Will Graham (The Pie Maker as a profiler?), but there's the possibility Pace still might appear in future...
Bryan Fuller originally wrote Dr. Du Maurier as an older woman and hoped to cast Angela Lansbury. When scheduling conflicts made this impossible, NBC recommended Gillian Anderson. This modified the storyline slightly; instead of being retired due to age, she left her practice for other reasons.
Fuller told the A.V. Club that he had originally planned to kill another supporting character, who he refused to name, at the end of the season rather than Abigail Hobbs but decided that this character wasn't yet developed enough for their death to resonate properly.
What May Be: Fuller has stated multiple times (and has extended an offer) that he'd like the incomparable David Bowie to play Hannibal's artist uncle Robert, the only stable parental figure in Hannibal's life after his parents were slain by Nazis. Who can tell in what capacity Robert might appear in the show? In any case, it'd be terrific to see Bowie interacting with Mikkelsen...
Fuller has mentioned that, assuming everything lined up properly, Chi McBride would be his top choice for the role of BarneyMatthews. He has expressed interest in working with a number of actors with whom he has past experience, specifically naming Anna Friel and Kristin Chenoweth.
Caroline Dhavernas was offered her choice of Freddie Lounds or Alana Bloom.
Tobias Budge was originally intended to be Jame Gumb, a.k.a Buffalo Bill (much as Franklin was supposed to be Benjamin Raspail), but when they couldn't get the rights to the character, they decided to rework him into somebody completely original.