So I sought some advice from a professional VFX artist and he recommended that I export a frame at the point where the dagger exits the front of Jon's throat, I mask out just his throat, move that into a seperate comp and animate blood trickling down it. I then put it back into the original footage and motion track it to his throat.
The reasoning for this is that Jon gets stabbed and does this really primadonna fall to the ground, his neck however maintains more or less the same shape and size as he falls sideways out of frame.
I was wondering if anyone can help me get started on the blood trickle effect. I have some nice Alpha footage of blood, but nothing that resembles a trickle unfortunately.
Create your own blood trickle- put some red food coloring in water, mix a touch of black or dark blue, corn syrup and thickener (here's a bunch of other recipes: http://www.wikihow.com/Make-Fake-Blood ), fill a baloon (white or green, matte finish) and stab that. You can get some pretty decent elements with any HD camera/DSLR.
I saw on a SFX channel on Youtube about using a 2 Litre bottle as a mould for a neck, use modelling putty to create a kind of skin, then just drizzle fake blood down that. Seems like it would get results!