Ain't It Cool News: The best in movie, TV, DVD, and comic book news.: "So, one of the first things that I recommended, aside from us spending a lot of time designing head hits and squibs that were non-explosive, that had air charges in them, I said, 'Listen. You forget that we have a great tool at our disposal. You set up a greenscreen and we shoot a bunch of blood sprays against green and you can comp 'em in and stick 'em in wherever you want.' And I'll tell ya'... they worked unbelievably well. You get really good, realistic blood sprays and the head hits look good and they're dramatic enough that they look just like a practical head hit."