What is Gelatine?
What is it?
You don't want to know. Seriously.
Ok. Well it's the same stuff that goes in Jello (Jelly for the Anglo-Saxons). It's a by-product of cattle. Meaning it's made of boiled down cow bones and skin. Gross, but really really useful stuff, and hey! You are here looking for gore, so maybe a strong stomach should be required.
Some vegetarians will not use gelatine products, and vegans will not at all. If people have leather shoes, likely they don't have a problem with it.
Why is it useful?
Professional make-up artists use Latex to make their monsters. Problem is latex is horrible stuff. It's rubber and even if the fumes aren't bad enough, the use of it with your household kitchen stuff will likely render them useless.
Gelatine can be used as a pretty good approximation, especially for prosthetics (think fake noses) and skin. It takes makeup really well, can be mixed and made with no extra equipment or fumes, is pretty hypo-allergenic, and really quite cheap.
Where do I get it?
Although you can buy little packets in the supermarket for a couple of dollars, you can usually get 10 times that amount for the same price in a "bulk barn" or any of those 'scoop and weigh' emporia. Purists will say to get 'high-grade' material for prosthetics. All I will say is get uncoloured, unsweetened, powdered gelatine. The stuff I buy is cheap and nasty but does the trick.
Watch 'mythbusters'? Its the same stuff they use for their 'ballistics gel' for the most part.