Here and there at the dark windows, Harry saw faces
faces that bore no resemblance at all to the painting of the mermaid in the prefects' bathroom
The merpeople had grayish skin and long, wild, dark green hair. Their eyes were yellow, as were their broken teeth, and they wore thick ropes of pebbles around their necks.
As we observe Harry observing the merpeople in Chapter Twenty-six, we have a wonderfully shocking vision of the unexpected. In contrast to our expectation of a beautiful, shapely, stereotypical mermaid like the one that Harry sees in the painting in the prefects' bathroom, we see a village of hideous, crusty creatures. They are not remotely what we expect Harry to find at the bottom of the lake. Mermaids, the ultimate illusion of beauty, can in fact be quite ugly. This disenchantment parallels many of the coming disenchantments, such as Mad- Eye Moody's revelation that he is the villain responsible for placing Harry directly within Voldemort's line of fire. As shown in this passage and others, reality is rarely how we imagine it will be.