When that mother and infant lock eyes, and the infant's old enough to have a social smile, what happens -- spontaneously -- is the eruption of joy on the part of the mother.
当母亲和婴儿闭上眼睛， 而且当婴儿大的能够做出笑脸时， 所发生的 -- 很自然的 -- 就是母亲乐趣的爆发。