The phantom hand
At first glance, this picture appears to be of four young boys having the best time of their worry-free lives. However, upon closer inspection, you’ll notice that a thumbs-up sign is floating in the background, just above the left shoulder of the kid on the very right.
Imagine taking a quick photo together only to discover that a mysterious phantom hand was right behind you. The likeliest possibility is that the kid on the far left super-extended his left hand, but that doesn’t account for the angle of how the phantom hand appears. It doesn’t seem to be ghost-like either, but you never know.