Wrigley's

Question

I was quite excited to hear that Wrigley's gum is kosher so I quickly went to their website. They say that their gum has glycerine in it. And as I am sure you are well aware the cheapest and most productive glycerine comes from the fat of animals. Without "proper" supervision how can a consumer be fully sure that this product is kosher. I mean no disrespect or that I don't trust you, I'm just a very curious person in general.