What's this?

Over the last couple of days, Kieran has started asking for the names of things. At least, that's what I assume he's doing. He'll hold the thing up (or pat it, if it's heavy), look at me intently, and say "ah ah ah." If I don't do anything, he'll keep doing it. If I say the name, he'll relax, give a contented, satisfied smile, and go on to something else.