Depending on who you talk to, the standard taco can come in many forms.

But the best rule is that anything can be a taco -- all you need is a tortilla.

In Mexico, where the taco was born a long time ago, tacos can get crazy. Everything from chicken and insects to an entire cow is rolled up, smothered with cheese, salsa, guacamole, lard or beans (or all of the above) and chased with a delicious beer (which might just be the most important ingredient of all, come to think of it).

As for the cow: "Everything is used and it all tastes great. Would you like an eyeball taco? Sure, just tell me which youd like -- the left one or the right one," Daniel Gonzalez, a taco maker at Los Gueros in Mexico City, describes in "Tacopedia: The Taco Encyclopedia ," Phaidon's definitive taco manual.

"Customers order the eye, brain and tongue tacos more than anything else. They just fly out the kitchen. Really, those eyeball tacos fly! Honestly, I have no idea how many cow heads we go through in a day.

Of the 549 edible insects recorded in Mexico, which ones do you think are used as taco meat? All of them -- ants, grasshoppers, jumil beetles, maguey worms, crickets, eggs, larvae, ticks and caterpillars are boiled in salted water or cooked on a griddle. If you want to show off, there is nothing classier than ant larvae, authors Deborah Holtz and Juan Carlos Mena write.

We'll take their word for it.

In honor of National Taco Day on Oct. 4, we present a quiz using facts from the book.

If you happen to have a copy, don't worry -- it's an open-book test.

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