What causes "stringy" melted cheese (and similar behavior in other materials)? I was wondering about this. What is the physics underlying the "stringy" consistency of melted cheese? That is, when the melted cheese is hot, and it is pulled apart, it forms strings of cheese.

This behavior also occurs with a number of other fluid substances. It seems to happen with polymer substances (like cheese which is made of proteins like casein, also plastics when melted), gums, etc. What is the technical term for this kind of behavior and what is the general mechanism by which it happens?
When cheese is heated to 140 degrees fahrenheit, the proteins line up in rows.  Soaking the cheese in a salt solution before pulling it helps to stiffen it and keep it pliable, as the salt neutralizes acids which could cause the long lines of protein to break.

Polymers, similar to cheese, can be stringy because their molecules are very large (macromolecules), and tend to entangle with one another.  @IanF1 is correct in saying this may be a chemistry question.  Here is a good explanation of polymerization:

http://courses.chem.psu.edu/chem112/materials/polymers.html