It´s a very strange-looking goose egg. Is it really shiny as in the photo? Are you sure someone isn´t playing a trick on you? Maybe there´s a little bag of chocolates inside!
It would seem my birds are reading these posts and are playing tricks on ME!....these last days I´ve had two tiny eggs from the chickens, and then the day after there was one tiny egg from a duck! I can´t post pic yet, as internet is very slow, but I will try next week. THEY LOOK LIKE THEY SHOULD HAVE CHOCOLATE INSIDE!