Why is some of the cheese you use not vegetarian?

Why is some of the cheese you use not vegetarian?
klinical

Our promise to bring you authentic food from across Europe means that occasionally they contain animal products because that’s what their recipe demands. For example, continental cheeses such as Parmesan and Grana Padano have what’s called PDO status, for “Protected Designation of Origin”. This means that in order to qualify for the name Parmesan or Grana Padano, it must be made using traditional methods and a traditional recipe, which includes animal rennet.