Does this bizarre trick work for you? And why does it happen?

Found this little oddity in my travels on the interwebs:

Stretch your arms in front of you; note that your fingers can reach approximately the same distance. Now rub one of your elbows. Stretch your arms back out again; the arm you rubbed will appear shorter. Shake your arm out and it’ll go back to normal.

I was skeptical, but I tried it and it actually worked for me. What gives?