NEW YORK CITY – We’ve had Doritos made into taco shells, Cheetos dust on mac-and-cheese and hot dogs stuffed into pizza crust, but those unusual pairings might just be the tip of the iceberg when it comes to fast-food novelties, The Motley Fool reports.

Chains from McDonald’s to Taco Bell to Burger King “need reasons to attract marginal customers,” said Scott Rothbort, chief market strategist for Seton Hall University. “They do so by introducing these limited time offerings of new products.”

“By associating a product with a highly craveable snack food, it puts in the consumer's head that their taco, burger, or fries are similarly craveable,” added Jonathan Deutsch, a professor of Culinary Arts and Food Science at Drexel University.

Deutsch pointed out that the competitiveness of the quick-service sector has heated up even more of late. That means that even more strange products will likely be available soon, as brand mixing continues.

Meanwhile, some fast-food restaurants are testing upscale items. McDonald’s recently piloted a Pesto Mozzarella Melt in Southern California, CNBC reports. “The pace of innovation at McDonald's seems to be accelerating,” said Mark Kalinowski, an analyst with Nomura.

Wendy’s has begun tests of Truffle Bacon Cheeseburgers and Bacon Truffle Fries in Tennessee and Massachusetts. “[They] sound like menu items that play to Wendy's brand positioning within the quick-service industry: 'a cut above' traditional fast food, yet still fully within fast food,” Kalinowski said. He attributed the premium offerings to a willingness of consumers to try new products, including millennials who have a more adventurous palate.