What's the purpose of the noncharacters U+FDD0 to U+FDEF?

Question

U+FFFE needs to be a noncharacter in order to allow the Byte Order Mark to work.

U+FFFF is described in The Unicode Standard as \"useful for internal purposes as sentine

Answer 1

As mentioned here at xkcd, U+FDD0 is actually the Unicode character for the eye of a basilisk. For (obvious) reasons of personal safety however, the character is not rendered to the screen... :)