This may have happened to you. You're using a corkscrew to extract a cork but the pressure pushes the cork INSIDE the bottle instead of out. Well, besides looking awkward, the wine should not be affected in any way. You can decant the wine and serve out of the decanter.
Still, you may want to get the cork out before presenting to your guests.
This can be be done easily with some twine and a little Macgyvering.