Watching zebras becomes a kind of meditation in this short poem. The speaker invites us to count the steps, the stripes, the tails swishing in the grass, and that counting slowly turns into a trance. Even the title plays with the idea: the zebra is the thing that calms.
The speaker seems relaxed and a little awestruck. The zebras are "walking ribbons of wonder," and they seem to wave even when standing still, as if the stripes themselves keep moving. In the second stanza the rhythm settles into "Black, white, black, white," a steady beat like a heartbeat or a rocking cradle. The bracketed "[ouslullaby]" is worth noticing: the word "wonder" slips into "wondrous lullaby," so the wonder turns into a song. The last line, "goodbye, goodnight," drifts toward sleep. The mood is quiet, hypnotic and soothing, and the repeating pattern makes you feel it as you read.