Nothing truly disappears. Every keystroke leaves an impression in the substrate of memory, a faint electromagnetic whisper that persists long after the visible text has been erased. The undo operation is a comfortable illusion -- it restores a previous state, but the act of having changed, of having existed in the altered state even briefly, cannot itself be undone. The ghost of every deleted word haunts the document forever, invisible but structurally present, like a healed fracture in bone that shows up on an X-ray decades later.