The BPRD complex was (according to Del Toro) was originally FDR's secret emergency bunker. The library where Professor Broom dies was the president's office and Hellboy's room (with the big vault door) was his fallout shelter, just in case Germany perfected the A-bomb first.

The soundtrack for this film includes a very unusual instrument: a precision-played theremin. The theremin was traditionally used to create spooky sound effects, but it this film it's actually used for playing melody, which requires exceptional playing skill. It's most heard in the scene where the portal closes and Rasputin dies. Submitted by Moose

The corpse that Hellboy reanimates in the Russian cemetery is voiced by Guillermo Del Toro (Director).

David Hyde Pierce dubbed the voice for Abe Sapien, but refused a credit.

Director Guillermo Del Toro didn't want to show a lot of blood during fight scenes, so he came up with ways of alluding to it. When Hellboy is fighting Sammael in the subway and he grabs the pay phone off the wall and uses it as a weapon, we see coins flying every time he hits Sammael with it. The coins represent the splatter of blood without actually showing it.

In angelic lore, Sammael is one of the chief princes of Satan. His name means "the poisoned angel."

When Professor Broom is leading Myer to meet Hellboy, they stop at a display area where Broom points out the Spear of Longinus. In a jar near the spearhead is what looks like a fetus preserved in amber liquid. This is actually a prop from Guillermo Del Toro's movie, "The Devil's Backbone." If you look carefully, you can also see the scarab prop from his movie "Kronos."

The Spear of Longinus (according to Christian tradition, a Roman soldier named Longinus used to pierce the dead Jesus at the cross), featured in the movie, actually exists exactly as it is depicted. The spear is a royal reliquary that can be traced back to around the year 900 (when it was most likely forged). The original spear is in exhibition in a museum in Vienna. http://www.nachlese.at/longinuslanze.htm.

The "gate" used to bring Hellboy to earth is very similar to the Revolution Studios (the film's studio) emblem. Submitted by Grumpy Scot

When they stop at the display area with the Spear of Longinus, look behind the spear; there's a golden box with two angels on top of it, fitting the classic image of the ark of the covenant.