She tells me that the water in the bathtub turned on by itself. The turning on was proceeded by a grumbling sound. The sound of the event was enough to startle the cats. She thought I had come upstairs to get a shower and she had not seen me. I tested the knob and found it is one of the older 80s styles that requires the knob to be turned from an "off" position to cold, then warm, then hot. She described the pressure of the output to be equal to more than just a little turn.
So, we might have had our first supernatural experience in the house. I don't have an engineering explanation of how the water could have turned on itself. I did take a shower in that bathroom in the morning, and left the knob in some almost on position, but pressure would not have turned the knob. Very strange... a mystery!