Re: What is it? "Uncomfortable" 9 month old...
Both of my kids, once they were 2 or so and able to communicate really well, flipped out over sock seams. Made some mornings into a headache, having to try several times putting on socks until the seams were in exactly the right place. (And last year I gave up and bought DS some seamless socks. But he has made peace with seams since then.)
Made me wonder whether that was behind some of the mysterious crying/fussing when they were babies -- when they were fed, taken care of, etc. but fussed anyway.