This scene is one of intense symbolism. Beloved, the mysterious girl sitting on the stump, provides a connection for Sethe to the older woman's dead daughter, who she killed in an attempt to protect them from a cruel master. Sethe, in her inner soul, believes Beloved to be a reincarnation or a ghost of that dead daughter. In the scene, seeing Beloved sitting on the stump causes Sethe to develop a sudden need to urinate:
Not since she was a baby girl... had she had an emergency that unmanageable. She never made it to the outhouse. Rigt in front of its door she had to lift her skirts, and the water she voided was endless... there was no stopping water breaking from a breaking womb and there was no stopping now.
(Morrison, Beloved, Google Books)
The moment echoes the breaking of amniotic sac that protects a baby during gestation. When a woman's "water breaks," the amniotic fluid that surrounds and protects the baby begins to flow out of the vagina; this is often misrepresented as a sudden and fast gush of fluid, but is often a slower seepage, easily controlled. For Sethe, the sudden need to urinate is symbolic for going into labor again; Beloved is "born" in this moment, and Sethe's body unconsciously repeats some of the physical characteristics of labor and birth. In fact, is is passing ordinary urine, but her mind and body associate the act and the appearance of Beloved with birth, further connecting the two women.