I remember hearing someplace many yrs ago that turtles are the smartest reptiles, but obviously nowhere near the IQ of, say, a dog. Not sure where that statistic originated from, but it makes sense to me considering they are one of the only animals on earth that did not technically evolve into anything over time. They are fundamentally the same now as they were a million yrs ago.
Their metabolism is really slow, so maybe they dream in "slow-motion?"
Sometimes I hear Sheba digging in her rocks at night too, but I don't know if she is awake when she is doing it because she sleeps on the mainfloor & I am upstairs. I know that if I try to catch her in the act, I will wake her up just by walking down the stairs.