When you first add oil to a pan, it will likely be comparatively stagnant, and will coat the pan as you progress it round. As it heats up, the oil will begin to transfer from the middle of the pan and break up into streams throughout the pan’s floor. If you tilt the skillet, the oil will shimmer like ripples in a lake, letting it’s time to add the meals. But when you discover smoke — a couple of wisps are okay — it is too hot and it is best to flip down the warmth.