So, what's the latest you've found that last hidden Easter egg?

I remember one year when I was still a pre-teen that weeks later we found one. My father and mother were both pretty surprised. They offered each other some good-natured ribbing about who miscounted during the harried retrieval process Easter morning. They also couldn't figure out why they hadn't picked up on its location by odor alone. Only, the curious thing was it didn't really rot; it just turned into a hard, rubbery ball. Seemed strange, but I guess under the right conditions, it happens. Anyone out there know the science behind that?