You know when you go to a show with a nonliteral title and there’s that awkward moment when one poor actor has to say the title and make the loopy thematic connection? Hate that. Thankfully, when the moment comes in David Lindsay-Abaire’s deeply affecting new play, Rabbit Hole, it’s one of pleasant transcendence instead of a neon-lit don’t-you-get-it sign. The cast is perfectly engineered to handle Lindsay-Abaire’s quick shifts from hilarity to grief: A simmering Cynthia Nixon and a nicely conflicted John Slattery play a married couple dealing with the loss of a son. And for her showstopping turn as Nixon’s brash but patient mother, you might as well just give Tyne Daly that Tony right now.