Otter and the Infinite Sadness

At a certain point, all babies begin to coo and gurgle, their first attempts to communicate thoughts beyond "I'm hungry (whaaaa)," "I'm dirty/wet (whaaaaa)," or "I'm tired (whaaaa)." Cooing implies (at least to me) a certain happiness, and Otter definitely has her happy talk. She likes to tell us, the ceiling fan, or even just the ceiling about her day, squeals with delight when we rub her tummy and talks up a storm on Poopy Towel.

But recently, she's developed another mode - cooing, but with great sadness. It's definitely not crying (believe me, we know all the incarnations of that) but a spoken lament that hints to a depth of feeling which simple words cannot capture. I'm not sure how widespread this phenomenon is, but when I did an online search (the way I now gather all info on everything baby) I came up with nothing. Apparently, when the world's babies coo, they do it with nothing but glee.

I wonder what Otter's Infinite Sadness is about - what thoughts are causing her such sorrow? I wish she could tell me in words I'd understand. But, be it a curse or a blessing, I suspect she'll never remember.