(at around 1h 19 mins) Before the battle for Conan's soul, as the wizard is painting his hands, we see that this warrior and thief has very nicely manicured fingernails- which we also see on Valeria after the battle as she is running her hands over Conan.
(at around 10 mins) Conan's mother is pointing the sword at the attackers' leader with both hands on the hilt. We cuts to a shot of Conan standing beside her holding her hand, then back to her with both hands on the hilt.
In the final battle, Conan and Subotai kill over 20 of Doom's mounted warriors. At one point, Subotai fires a single arrow at two attackers--and both go down. He could have only hit one of them, so why did the other fall, too?
(at around 49 mins) When Valeria reaches for the jewels after they first steal from the tower, her hand is faced downwards but when Conan grabs her and seductively moves the jewel over her, her hand is turned over so she can move her fingers towards the jewel.
When Thulsa Doom fires a snake-arrow at the four riders escaping below, they are riding camera-left to camera-right. A reverse angle shows Valeria reacting as she's struck on her right side. Yet when Conan removes the arrow from her as she's dying on the ground, she's at camera-left, he's at camera-right--and it's obvious he's removing the arrow from her LEFT side.
When the trio prepares to invade Doom's mountain, they camouflage themselves with 'war paint' (but Rexor recognizes Conan anyway), with black 'slashes' across their faces and torsos. Subotai adds cream-colored paint between his black marks, and Valeria applies it under Conan's left eye. But once inside, no one has cream paint--only black slashes and natural flesh colors.
In one of the takes in the deleted scene showing Thulsa Doom's henchmen killing King Osric, one of them stabs him in the back, but there was no blood. Reason is because the guard missed the blood pack.
(at around 1h 30 mins) While sneaking into the orgy, Valeria slowly and quietly makes her way over a low ledge on her way to the main area of the cave. At one point, her foot kicks a set of large hanging chains, causing them to swing. In the very next shot of her, presumably after only mere seconds of a cutaway shot, she is in the same position as last we saw her, but the chains are completely still.
(at around 1h 12 mins) When Conan is being beaten and tortured by Thorgrim and Rexor, in one shot you can just make out the bottom of Conan's father's sword positioned horizontally on the steps. A shot later, when Rexor and Thorgrim pick Conan up off the floor, the same sword is positioned vertically up against the edge of the stairs.
At various points in the movie the sound of the common loon (a type of duck) is heard. It has a haunting, mystical sound. The movie takes place in arid, desert conditions, however the common loon is a waterfowl that only inhabits lakes and other bodies of water. Loons would not be heard in the kinds of settings depicted in the film.
(at around 1h 35 mins) During the Orgy fight, one of the pillars has a crack visible before the warrior breaks it with his war-hammer. The pillar is initially cracked by the giant soup pot that Conan rolls down the steps.
(at around 2h) A few of the devotees holding torches toward the back in the night scenes at the end of the movie are swinging and looping their torches. Obviously they are having fun with the flame while they should be morning the loss of their leader.
(at around 9 mins) When Conan's father is killed in the beginning of the movie, an axe is left lodged in his back before he is attacked by dogs. When the dogs are attacking him on the ground, the axe in his back is gone and there is no sign it was ever there.
(at around 2h) After Conan cuts off Thulsa Doom's head and throws it down the stairway, the head is seen to stop rolling, still on the stairs. In the next shot, however, the head is not seen, but in later shots, reappears again where it had landed.