When a few cubic centimeters of liquid nitrogen are spilled in a pan or on a floor it forms a film of gas between the liquid and the surface. That gas provides effective insulation so the evaporation rate is considerably slower than you might expect. The droplets also have the tendency to pick up dust from the surface and as they evaporate the dust is concentrated often forming a tiny ball when the nitrogen has completely evaporated.

science-fun.org

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