four lean hounds crouched low and smiling the level meadows ran before.
Repetition's the name of the game in this stanza. Lines 1-10 set up a pattern: first Cummings introduces a rider, then the poem pans out to the hounds beside her, and then it discusses the deer that seems to be running with them. Lines 10-13 start that pattern over again. What we have now is repetition with only a very small difference. Can you find it? (Yes, we know, this starts to sound a lot like those puzzles on the back of a cereal box, but Cummings is actually up to something here.) See, the repetition lulls us into thinking that everything is static and unchanged, just like the picture that we referenced back in lines 1-3. But there are very, very slight changes that roll the scene along. Instead of merry deer running before the hounds, now level meadows stretch out before them.
Luckily, the level meadows still seem like a pretty pleasant place. (See Mr. Cummings? We can alliterate, too.)