Zebras are the subject here, but the poem is really about what happens when individuals melt into a group. The speaker watches them press together, tails and shoulders touching, legs crossing and interlocking, until the stripes stop marking out any single animal. The opening line pushes against the old idea that there is safety in numbers. What protects them, the poem suggests, is not size but blending in: they are "small, clever" and willing to give up personal space.
The speaker seems fascinated, even a little unsettled. The questions about a zebra with "three ears" or "six hooves" show how hard it is to tell one body from another. The mood is quiet and watchful, with a hint of eeriness. The closing image, of the herd "silently stamping no lone print," leaves us with something both admirable and slightly sad: safety bought by disappearing.