Can you tell me about the mysterious wooden plank Sai Baba used to sleep on? It sounds impossible.

Certainly. Chapter 10 of the Shri Sai Satcharitra describes this fascinating aspect of Baba's life. He would sleep on a simple wooden plank that was only four cubits long and a mere one span (about 9 inches) wide. This plank was not on a frame but was hung from the rafters of the mosque with old rags, like a swing. Miraculously, Baba would sleep on this narrow, suspended plank, often with lamps burning at his head and feet. As Chapter 10 notes, his movements were imperceptible; no one ever saw when he climbed up to the plank or when he descended from it, adding to the mystery of his divine nature.