A new one is something I can't easily describe, kind of like a really deep scowl with one eyebrow raised really high, the expression a mixture of surprise and horror. After pulling this face he raises one finger to his lips and gives a sharp "Shhhh!" in response to whatever you're saying. Because apparently "shhh!" is an appropriate response to "do you want strawberry or raspberry yoghurt?" "come in and wash your hands", "be gentle with your sister" or "it's time to go potty".
He doesn't always do the scowl though, sometimes he'll just scrunch up his nose instead. It's become a real habit though, he's constantly shushing me!! I guess it doesn't help that half the time I bust out laughing because he takes me completely by surprise with his forceful little "shhh!".