Karelian Birch Egg
Karelian birch, gold, silver, diamonds, enamel, by House of Fabergé, and Henrik Wigström
Drawing by Carl Fabergé, 1917

Unlike most Fabergé eggs crafted from precious metals and adorned with gemstones, original documentation indicates that this egg's shell was constructed from Karelian birchwood with a simple gold setting, likely due to austerity measures in place during World War I. The documentation also indicates that the egg opened, and that the surprise inside was a silver and gold mechanical elephant set with rose-cut diamonds. The egg was made for the Dowager Empress Marie Feodorovna, however, it was never presented, and is considered unfinished by some experts. This egg has been considered lost, however, in 2003, a wooden egg matching the description of this one was purchased by the Russian National Museum, and has been is now housed in the Fabergé Museum, but without the mechanical elephant surprise. It does have a key, possibly to wind up the elephant. See here.