In lieu of an introduction to today's featured research article, we give you one of our all-time favorite Monty Python sketches: http://www.youtube.com/watch?v=IqhlQfXUk7w Sideways walking: preferred is slow, slow is optimal, and optimal is expensive. "When humans wish to move sideways, they almost never walk sideways, except for a step or two; they usually turn and walk facing forward. Here, we show that the experimental metabolic cost of walking sideways, per unit distance, is over three times that of forward walking. We explain this high metabolic cost with a simple mathematical model; sideways walking is expensive because it involves repeated starting and stopping. When walking sideways, our subjects preferred a low natural speed, averaging 0.575 m s(-1) (0.123 s.d.). Even with no prior practice, this preferred sideways walking speed is close to the metabolically optimal speed, averaging 0.610 m s(-1) (0.064 s.d.). Subjects were within 2.4% of their optimal metabolic cost per distance. Thus, we argue that sideways walking is avoided because it is expensive and slow, and it is slow because the optimal speed is low, not because humans cannot move sideways fast." Related content: Seriously, Science?: How you walk differently with friends and lovers. NCBI ROFL: Walking with coffee: Why does it spill? NCBI ROFL: When it comes to walking backward, practice makes perfect.