I'm hoping this is just a case of me reading/ comparing what other babies are doing, but I'm not sure. DD will be 4 months on Friday and I keep reading that she should be pretty social by now. She may or may not smile at a stranger, it's completely inconsistent. Mostly she just gives them a good stare down. She smiles at me and DH all the time, though. Is this cause for concern or are some babies just not that friendly?