Today B figured out how to put his hand to his mouth. He's still working on extending his thumb, but it's a good start. Maybe in not that long we won't have to tear across the house every time he knocks the pacifier out of his mouth during a nap and starts screaming.
He's also inordinately proud of himself whenever he does it; you can see him grinning all around the fist. He's gotten more sociable in general, smiling even when he doesn't want something (that desperate wide-eyed raised-eyebrows smile is so funny and pitiful) and doing a whole body wriggle when he's happy to see someone.
B is also so much more physically together than C was at this age; makes it so much easier to take care of him (although it will also make it much harder shortly when he starts turning over and becoming mobile). Now if he would only sleep when we want him to.