The 3:15 AM Ritual

Every night at exactly 3:15 AM, a heavy, rhythmic thumping from the apartment below wakes me up. *Thud... thud... thud.* I finally called the police, but they found nothing; the frail old woman living there claimed she sleeps soundly and heard no such noise. Driven by sleep deprivation and paranoia, I crept downstairs last night and peered through her keyhole. In the dim moonlight, I saw her silhouette standing in the center of the living room, her body violently jerking forward and backward in perfect, unsettling synchronization with the thuds. Tonight, armed with a baseball bat, I banged on her door furiously. When she opened it, I froze, dropped the bat, and my face burned bright red as I stuttered out endless apologies. What was she doing?