It's obviously impossible to bite into a neck artery with normal human teeth sets.
Various mods have vampires with elongated (sometimes extendible) canines or even hollow teeth (though both of these would be very vulnerable), but even the mods don't really make it much easier - you have to add in the ability to almost dislocate the jaw and/or retract the lower jaw to be able to get a tooth into the vein, something which would if properly recorded make you look less like sexy vampire and more like Monty Python Upper-Class Twit.
Yes, it would be fairly easy if they went for the wrist, say, or the big toe, but it does always seem to be the neck, for some reason.
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