I think I have told this one before, but we came home from work one day to find an egg on the kitchen floor. Yes, a perfect chicken egg. No cracks on the shell or anything. Which is even weirder because I don't keep eggs in the house; we use liquid eggs in a carton.
We have a large, open kitchen so DH and I both got on our hands and knees and looked under the baker's rack and microwave stand. We scratched our heads over that but ultimately put it in the trash.
A little later that same evening I walked out in the kitchen and found...another egg. On the floor. In the middle of the room. I checked the trash can and the original egg was still in there, so it was definintely a second egg. To this day we cannot come up with a reasonable explaination for their appearance.
We still joke that we have the world's only egg-laying cat (male, at that).