SortStack #1786 — 2031-04-30

By speed · Order from slowest to fastest.

1. The growth of a cave stalactite 0.1 mm/year

   Most stalactites lengthen by less than a tenth of a millimetre a year, dripping mineral by mineral over millennia.

2. A giant tortoise 500 m/h

   Giant tortoises can live over 150 years, ambling through more than a century of slow, steady days.

3. A chicken foraging 3.6 km/h

   Chickens can recognise over a hundred individual faces, both other birds and the humans who feed them.

4. A red fox 51 km/h

   Foxes may use Earth's magnetic field to aim their pounces, lining up on prey hidden under snow.

5. A racing greyhound 76 km/h

   Greyhounds reach their top speed in just a few strides and spend much of a sprint completely airborne.

6. A record tennis serve 270 km/h

   The fastest serves leave the racket so quickly the returner must react before the ball has even crossed the net.

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