There is no benefit, no reward, no ultimate reasoning beyond 'I want to shake this street sign". As I looked down, I was right, and the kid was grinning like cr

There is no benefit, no reward, no ultimate reasoning beyond 'I want to shake this street sign". As I looked down, I was right, and the kid was grinning like crazy. Actually, there was benefit and reward for the kid shaking the sign. The kid is trying out some things, learning about the world. Answering questions about the world such as: How strong and stable is this sign? Can I shake it like a tree branch? What sound will the shaking make? How strong am I? Am I strong enough to move this sign, even a little? You likely have a good estimate of your own strength, and the how well the sign is installed, so you don't feel much need to shake it and learn its and your own limits. I still do similar things. I tend to tap / rap with my knuckles things like steel stair railings. Some of them can make interesting and long-lasting notes, while with others the best you can get is a dull "thud".