Knives are an essential tool to a killer in a slasher film. Freddy Krueger has knives for fingers, Ghostface kills with a knife, and the king of killers, Michael Myers, hasn’t gone anywhere without a knife or other sharp, pointy object in over 16 movies. 

It’s the perfect weapon—but how do you make it look practical while keeping your movie victims safe? Sure, you can use a retractable knife, but you could make a cooler shot with a little bit of movie magic. To celebrate the release of Halloween Kills, Film Riot showed us how to recreate Michael Myers’ stab effect using mostly practical elements and a few digital elements to sell the scene.

Check out their full video below: 

Here is what you’ll need: 

The first thing you’ll need to do is set up how you are going to shoot the scene in an order that will allow you to get everything out of the way before adding in any blood. This will keep your set clean and allow you to have multiple takes without resetting constantly.

You will need to get a shot of a real kitchen knife separately attached to a magnet and use some moving lights to change the reflection of the knife. This shot will be very helpful when it comes time to digitally edit the knife into the scene since using a real blade that will be roto out later makes it much easier than using a fully CG knife.

Ben_nye_thick_blood_on_prop_knifeBen Nye Thick Blood is perfect for covering any type of surfaceCredit: Film Riot

Practical effects

It is time to add the blood once you have all of your shots. The best way to recreate a bloody knife that has been pulled out of someone’s body is by using thick blood, a fake blood with a gel-like consistency that will stick to the finish of the prop knife. 

Now comes the messy part. Grab the second prop knife, and chop off most of the blade, leaving about an inch or two. Then, sand down the remaining blade to make sure it is fully safe. This dull knife base will be what your killer will be stabbing their victims with, and the knife will be digitally added on later. 

Although stabbing someone in the shoulder or leg won’t create a lot of blood splatter, it is a fun, practical visual effect that can be created by running a tube up the killer’s sleeve and securing the tube to the side of the knife base that is opposite of the camera. The tube should come almost to the edge of the knife’s base while allowing enough space for the blood to shoot out. The tube should go through the killer’s sleeve and out of the costume, so someone on the side can push the fake blood out of the syringe and into the tube. 

Before the cameras start rolling, make sure to push the blood through the tube so that way when the killer stabs, you can push the blood through with ease and hit your mark. At this point, make sure there is a tarp laid out under the characters to keep the area you’re shooting in clean. 

Start rolling your cameras and have the killer stab the victim with the sanded-down knife, squeeze the blood through the tube to add some extra gore, and cut the camera. 

It’s time to digitally add the cut-down knife to the stabbing shot.

Adobe After Effects

To add the full knife back into the shot, bring the footage into a new comp in Adobe After Effects, and create a new normal that you will use for the knife track. Right-click your footage, and select "track motion." Move the tracker to a part of the hand and the knife handle since the section of the blade has some reflections that could ruin the track. You can also add a "rotation track" and move that to a similar area as the "track motion."

Since the speed of the knife entering the victim is too much for the tracker to follow, you will have to manually move the trackers for each frame. Once the knife is in the end position, you can finish tracking each frame. Now that you’ve finished tracking, it is time to edit the target, making sure that the "no layer" is selected, then click "apply."

When you scrub through the shot, you can now see what the track is like during those frames, and manually adjust the rotation values of any frame where it doesn't rotate correctly. Try using the angle of the motion blur in the footage as an example to try and match the rotation correctly. 

After_effects_knife_swapUsing Adobe After Effects to digitally add in the knifeCredit: Film Riot

Remember that real knife footage from earlier? Roto out the blade section from that footage, move that anchor point to the base of the knife in the scene, change the position scale and rotation to match. Add any color effects that you need to use to make the digitally added knife match the main scene better. You can also use the "feathering mask" set to subtract to blend this section of the blade into the original footage. Now, link the knife to the track null and enable "motion blur."

For the last few frames—when the knife enters the victim’s chest—you can duplicate the footage by bringing it to the top of the comp, and add a mask, some feathering, and keyframe if needed to the part of the body the knife is entering. Then, trim the layer to just those few frames where it covers the blade, trim the knife layer to finish once it is in the end position, and then add some gory, stabby sounds. 

Now you have a simple way to create a violent, convincing, and dramatized stabbing effect. This brief effect is over once the knife makes contact with the victim, so it is a pretty easy effect to pull off well. Your stabbing effect may rival that of some of the greatest slasher killers out there, so try it out this Halloween. 

Let us know what you think of this effect in the comments below!

Source: Film Riot