Hột vịt lộn is called "Trứng vịt lộn" at Northern Vietnam.
Vit means duc. Trung means egg.
They called "balut" in Phillipines.
Chinese called them "máodàn" or "sǐtāidàn".
I would not show how to eat it but you can search on the net.
Almost 90% of Vietnamese (or I heard Filipino) like this.
They consider Hột vịt lộn contains high protain and etcetra.
There are many weired dishes in Asia orworld wide. These are not common and most of them are not deliscious.
Hoever, Hột vịt lộn is very common and you can often see those at street stands in Vietnam.
I wanted to get feeeling why they like Hột vịt lộn.
I have eaten them dozen of times and I think I am getting used to eat them.
Balut by Wikipedia