What Magic Drum?

A poem by William Butler Yeats

He holds him from desire, all but stops his breathing
lest
primordial Motherhood forsake his limbs, the child no
longer rest,
Drinking joy as it were milk upon his breast.
Through light-obliterating garden foliage what magic
drum?
Down limb and breast or down that glimmering belly
move his mouth and sinewy tongue.
What from the forest came? What beast has licked its
young?