This may be a very stupid question but I've got no scientific background so stick with me. When talking at the level of atoms or atomic particles, what is meant by the notion of heat "transferring" between particles? People often use language that suggests heat is a thing or a kind of particle in itself. Is this literal or is heat better understood as a kind of effect particles have on each other? Whichever case is true, how do we know? The same thing applies to kentic energy - when one particle causes another to move, is something literally being exchanged between them?