Saul notes that the white men brought bottles, "Spirits", what his mother called "bad spirits." How did the "spirits" cause the adults to act?

From the text:

When they returned they brought the white man with them in brown bottles. Spirits, Naomi called them. Bad spirits. Those spirits made the grown-ups move in strange, jerky ways and their talk was twisted. I fell asleep to evil laughter. Sometimes my mother lurched to her feet and danced around the fire, and the shadow she threw against the skin of the tent was like the outline of a skeleton.