Nina measures how tall Elmo and Rosita are with a growth chart that uses smiley faces; Big Bird wants to see how tall he is, too.

Idris Elba returns as John Luther, the near-genius detective waging his own war on crime. This series sees a twisted fetishist targeting young women in London. Luther is convinced the man will strike again, but when the detective is ordered to investigate another case, the chances of catching the killer start to fall. But Luther's biggest threat could be closer to home, when it emerges that his own colleagues are willing to break every rule in the...

Forty million years ago—long before birds, bats, or flying pterosaurs—the skies were dominated by insects. Unlike every other subsequent flying animal, insect wings did not evolve from modified limbs; insects kept all six limbs and added wings. Explore a variety of flying insects and learn the unique physiology that gives them such precise control and maneuverability in the air.