It's the first thing most people do in the morning. You roll over, stretch your arms over your head, and give a good yawn. Then you move toward coffee or Facebook or sniffing your armpits to decide if it's a shower day or whatever it is that you do next.
But why does that stretch come so instinctively? And why does it feel so good? Well, Sci Show has an answer. It's called pandiculating. It's the act of stretch and yawning at the same time, usually right when you wake up in the morning. Cats and dogs do it too, and there's good reason for it.
That full-body stretch wakes your muscles. Your brain may be awake (even if it doesn't feel that way), but your muscles have been inert through most of the night and need a good stretch to get going. Stretching loosens and realigns the muscles. It also helps circulation, getting your blood flowing after your heart spent the night moving a little slower than it does during your waking hours.