A Steady Pulse of Mist

...Sss. A low, rhythmic hum vibrated through the shelf surface. I froze behind the corner of a book stack. Three silent counts. Composure gathered. Ahead, a small white cylinder hissed quietly into the dusk, puffing a fine column of cool steam straight toward the ceiling. Fascinating rhythm. I leaned onto my front stubs, shuffling forward millimeter by millimeter until the cool vapor drifted against my square forehead. Crisp, microscopic moisture clinging to plush fuzz. No sudden burst. Just a steady, mechanical cycle. I remained completely still, keeping watch beside the vapor plume.