Visible crew/equipment: As the camera moves in on the bull that is about to be grabbed by the vampire, if you look under the bull, you can see two men hiding behind it. You can see their legs. They are probably there to keep the bull standing still. When it cuts they are gone. (00:26:05)
Visible crew/equipment: When Anna picks up the sickle you can see a shadow moving. It has to be a crew member, because when it cuts, we can see that no one is standing anywhere near her. (00:27:10)
Visible crew/equipment: When Van Helsing and Anna swing up in the balcony with the rope and Van Helsing pushes Anna against the wall, you can see a shadow move away on Van Helsing's left side. They are supposed to be alone on the balcony and the shadow doesn't match their movements. (01:23:40)
Visible crew/equipment: When Dracula says "You can't kill me, Victor... I'm already dead!" in the beginning, pay attention. As the camera dramatically moves towards the two men, you can see the shadow of the camera appear on the lower half of Victor's face. It's not Dracula's shadow, because it appears after Dracula moves right in front of him, and perfectly coincides with the camera movement. There's also a brief flash of lightning, and the lightning shows that the shadow is very "boxy," unlike a human shadow.
Answer: After being killed - "murdered" as Dracula stated several times - by Van Helsing, Dracula made a deal with the Devil to regain his life. Carl tells his story when telling Van Helsing and Anna everything that he has learnt.