He said twice over before he knew himself:"Can't a man speak of his own child he's lost?" (36-37)
The man feels that, for him, the subject of his dead child is taboo. Also note how he edges around the concept of "dead" without actually saying the word "dead." This is something that happens often in this couple's communications. No one wants to say "dead," probably because it somehow makes the death more real.
Her fingers moved the latch for all reply. (47)
The woman in this poem does a lot of nonverbal communicating. Instead of replying to her husband with words, she'll just do something subtle, like stiffen her neck, or move the latch of the door. This could mean a couple of things: (1) she's so sick of not being able to communicate with her husband that she feels he's not even worthy of words, or (2) that she's dismissing him without actually coming right out and saying it.
"I don't know how to speak of anything
So as to please you. […]" (49-50)
This couple's conversation is so stilted that the man feels that he can't speak to his wife at all. These lines put all the blame on her, though we have a feeling that he's partly at fault here, too. In the rest of the poem, he shows us how he pretends to try to listen to and support his wife without making much of a real effort at all.