Well, you see, flames naturally rise at 24 fps in reality. That is why old films use that rate, so the fireplaces in the ever-popular Victorian dramas/biblical epics would look natural on screen.
With new HD technology, frame rates are higher, so the natural rate of rising flame and the "film" are now out of synch. On a sine wave graph of the respective frequencies, you would clearly see how tiny black holes form at the vertices of the colliding waves. These tiny black holes suck the flames back down.

Here ya go, you earned these.