My 10 months old son had a difficult day last Sunday. First he fell (nothing serious), then he bit down too hard on one of his toys, then he bonked himself in the head with the spoon which we have him as consolation. ( He sometimes prefers dinnerware to toys.)
On Monday, he woke up with a very serious demeanor. I imagined him to be contemplating the years ahead together with his discovery of how cruel unforgiving the world can be. To the surprise of my wife and I, his air of seriousness did not abate. He took no solace in toys or baby sounds.
Only in the evening, did bath-time finally break the spell, and he again started smiling and laughing.