Basilisk

The house-elves were usually sent in the early morning to collect the eggs, but that was still a few hours off. No doubt, if he only took one, no one would notice.

"Wingardium Leviosa!" whispered Slytherin. A hen levitated, and he eagerly reached into the nest. It took but a minute to find the egg, and he cradled it gently. Common sense told him he would only have one chance to steal from Hogwarts, and that he must be careful in what he took.

But Slytherin was confident, and he quietly slunk off the grounds, already looking for a toad.