Wow, thank you thank you thank you my friends for wonderfull words. Yes, it is goose egg, it is carved with dentist tools. It was my first try with egg carvings, after this I made several sculptures with ostrich and goose eggs. It is not too hard to do something like this, but you will need a looot of patience and skill for it.
I know a potter who does porcelain pieces with a similar feel, taking a very thin thrown pot (leather hard clay) and carefully carving out patterns as the clay dries. Takes an amazing amount of patience.