Ever do a double take when you hear the person standing in front of you ask for the Pizza Sub at Subway or a Quesarito at Chipotle?
Many of these "secret" menu items began as items concocted by restaurant employees or customers. Others are discontinued former menu items that are still available for those in the know.
Restaurants sell these off-menu items and use them as marketing tools that make customers who feel like insiders want to share the information with their friends.
But in a contradictory move, many of these companies are showcasing these secret menus on their own websites. Mama Fu's "Black Market Menu" is one example. (The company's Ma La Stir Fry is shown here.)
The trend is being driven by restaurants that want to speed up the process for filling complicated orders and to cater to dietary preferences.
Click ahead to see some of the most interesting secret menu items we could find.
—By CNBC's Katie Little and Sarah Whitten
Updated 4 March 2016
Posted 8 April 2013
Price: $12.49, plus tax
If you are ever in New York City, stop by the Red Lobster in Times Square for a "Bey" Breeze.
The play on a Bay Breeze may not be on the menu, but the staff will know exactly what you're talking about. The new drink was renamed in honor of R&B singer Beyonce, who mentioned the lobster restaurant in her song "Formation."
The mention boosted Red Lobster's sales 33 percent over Super Bowl 50 weekend, company brass said, and sparked this secret menu item.
Price: $6.25, plus tax
It's the joining of two fast food heavyweights: pizza and sandwiches.
Although Subway's Pizza Sub used to be available on its official menu, customers can still order the sandwich with spicy pepperoni, cheese and marinara sauce. They just have to ask.
Price: $8.55, plus tax
Twice a year, Mama Fu's releases a new seasonal Black Market Menu as a way to test ideas. Some of these dishes could end up on the permanent menu.
This season's items include the seared sesame seed-coated tuna dish shown here.
Price: about $12, plus tax
What's better than a burrito? A quesarito, a cheese quesadilla wrapped around a burrito, for the same price.
While not every Chipotle fan on Twitter reported success ordering the item, those who did left happy.
User JParksTFm wrote: "Chipotle has a secret menu option, and it's the greatest thing EVER. Game changer. #Quesarito"
Price: around $6, plus tax
The not-so-secret menu was first pioneered on a large scale by fast food chain In-N-Out. Carl Van Fleet, vice president of planning and development, said the company doesn't see itself as having a secret menu but rather a willingness to fulfill orders the way the customer wants.
Several items from its not-so-secret menu — including the 4x4, a cheeseburger with four beef patties and four cheese slices — have inspired a fervent following.
"Over the years, many of those variations were given names, usually by the customers who frequently ordered their burger that way," Van Fleet said. "We never set out to create or pioneer a 'secret menu.' Some of the names for those variations just stuck."
Price: $6.69 for a Venti, plus tax
For the price of about six Twix bars, you can order a Frappuccino version of the chocolate candy at Starbucks, which is a caramel frappuccino with a pump each of caramel and hazelnut syrup, java chips and drizzles of caramel and mocha . Because the company lets customers completely customize their Frappuccinos, the possibilities are endless, but, you'll have to dictate the recipe to your barista.
Other favorite Frappuccino flavors include cake batter and cookies and cream.