My boys have a special understanding of each other. It's like life is an inside joke, and every one is "outside" except them.
They are best buds, brothers.
It's a little different than many brother's relationships because they are 8 years apart and my youngest is just 18 mos. old today. But they're brothers just the same.
Even when my youngest was an infant, his older brother could make him laugh and giggle when no one else could. Or he could immediately distract him from a fit when no one else could.
One of the most entertaining things in my life is watching these two interact.
I may not know why they are laughing. I probably don't want to. But it's still music to my ears.