So, Dementors Part Deux.

First, because someone had to say it:

Harry took all the silver emotion that fueled his Patronus Charm and shoved it at the Dementor; and expected Death's shadow to flee from him -

-and as Harry did that, he flung his hands up and shouted "BOO!"

The void retreated sharply away from Harry until it came up against the dark stone behind.

In the hall there was a deathly silence.

...And to everyone but Harry, that deathly silence seemed to say "Please do not punish this one, my Dark Liege!"

Harry turned his back on the empty void, and had a moment to wonder why Dumbledore and Lucius were making such odd faces before the Aurors acted on reflex.

(I guess Dementors aren't that smart.)

Secondly, I noticed that Harry's first Transfiguration lesson includes a photograph of a Dementor. What would that look like? What does Harry see, compared to everyone else? Why was he asking all the other students what they saw in the Patronus lesson without ever once thinking of that photograph?