from the creator's comment:
"If you're about to leave a comment saying that faster creatures aren't actually less efficient, read this first. I presented that part a bit strangely. At 2:14, I say moving quickly is less efficient, giving the example of a creature moving a unit distance in half the time, using twice the energy. Then, at 4:53, I show a formula for the energy cost per unit time, which depends on the square of the creature's speed. I gave distance per time, energy per time, and distance per energy at separate parts of the video, and that was confusing. So here's a more explicit summary. If we double a creature's speed... - its distance per time is doubled (the definition of speed) - its energy per time is quadrupled (because it depends on the square of speed) - its distance per energy is halved: (2x distance per time) / (4x energy per unit time) That last bullet is the "efficiency" from the video. With its starting energy for a day, a 2x-speed creature can only travel half the distance."