Can you touch your tongue with your elbow?
The first is the length of the clavicle plus the length of the humerus, which together forms a distance to the elbow. Even though you can adjust the angle between these two lengths, you cannot handle it. Because this is a longer distance, you want to make it as short as possible. (Try moving your right arm to the left in front of your face, which minimizes the length of the clavicle).
The second is the length of the cervical spine, plus the length of the jaw, plus the length of the tongue. Because this is a shorter length, you want to make it as long as possible; by making all lengths into a straight line.
Even though the configuration is optimal, most ordinary people can’t manage it. I can get my tongue as far as the inside of my elbow, but not the outside. Some people with hypermobility syndrome may be able to manage it; and some people with their anatomic anomalies. But for most of us, geometry is against us.
This is obviously not so impossible for some people. Supposedly, Guinness World Records receives about 5 requests a day from people who think they are special just because they can lick their elbows