The saber-toothed cat Smilodon fatalis roamed America during the Pleistocene before going extinct about 10,000 years ago. A top predator, Smilodon seemed to use its sabers to slit the throats of its prey (terrifying!). A new paper published in the journal PLoS ONE investigates how the sabers developed — and found the sabers grew almost twice as fast as modern lion canines.