First-time visitors to the Philippines should expect a good-natured hazing from their local contacts, one that comes in a culinary dare. No trip to the Philippines would be complete (they'll say) without eating balut!

What is balut? What makes it so special? And why is it constantly being pushed in the faces of foreign visitors by well-meaning Filipino locals?

Balut is very simple: it's a fertilized duck egg, the embryo permitted to develop in the shell for eleven days, upon which the whole egg is boiled.

Crack the shell of balut open, and you'll find a partially-formed duck embryo soaking in a pocket of broth and surrounded by the usual components of a hard-boiled egg.

Balut is sold on the street by roving mambabalut (balut sellers). The stuff is dispensed from cloth-covered baskets that keep the balut eggs warm; you'll be given rock salt to sprinkle onto the egg once you've cracked it open.

Its appearance does not significantly improve the appetite. Partially-formed embryo looks ragged and sad, a sorry almost-featherless imitation of a duckling stuck onto a yolk. Eat it and expect to encounter embryonic guts, cartilage, maybe the odd feather as you chew. You'll be expected to eat the duckling first, the rest of the egg afterward.

Balut is more popular in some quarters than others. Filipino men swear by its aphrodisiac qualities, and often eat it while drinking beer with friends. (MNL Boutique Hostel in Manila, for one, allows its guests to try balut in this context - read our guide to drinking in the Philippines.) Other Filipinos would rather just eat balut's unfertilized counterpart penoy, which is sometimes coated with orange-colored batter and fried to make the artery-clogging street food called tokneneng.

So should you eat balut? There's no good reason not to - it's not known to cause any allergic reactions, and you're not expected to eat it in large quantities. For the purposes of tourist hazing, eating one will do. If you don't like it, let's hope you at least have some amusing pictures of the experience to share on Facebook. If you do like it... well, have as many as you like, you're in the Philippines, after all.