Everything seems normal...
The light is getting a little dimmer. It seems as if a cloud has passed over the sun.
Odd, it is still getting dimmer. It looks like it's almost twilight now.
Suddenly, in the dim light, you notice that the pool is glowing. Or at least the mosaic at the bottom of the pool is glowing. With a faint, yet undeniable blue
luminance. And it's getting stronger.
You stare in facination at it, almost oblivious to the fact that there is now almost no light comming in through the windows; it is pitch black except for the blue light
streaming up from the bottom of the pool...
The two fish depicted in the mosaic seem to almost writhe and twist as you watch.
You feel a faint tingling run up your spine.
Suddenly as quickly as it began, the mosaic dims, and the windows become bright again, as if whatever cloud obscured the sun has passed.