Why is watching something over a hot stuff (BBQ, exhaust pipe…) making it blurred and seemingly moving?

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Why is watching something over a hot stuff (BBQ, exhaust pipe…) making it blurred and seemingly moving?

In: Physics

Refraction. The air has a refraction index, and the hotter the air, the larger this gets. The light “bends”, refracts, at these pockets of air and therefore make the vision through them blurry. It is actually similar to why stars seem to twinkle.