While fast food chains in the U.S. are thinking up ways to outwit each other in the chicken sandwich wars, over in Spain, another chicken-based rivalry is taking place. 

KFC in Spain has come up with an intriguing way to promote its latest limited edition menu item—a chicken sandwich that replaces the bun with two pieces of fried chicken. It's enticing employees of any rival fast food chain to taste the product, known as "La Infame," anonymously and in secret this weekend, for free. People can apply via a telephone number and a website and, once they've proved they do work for a rival, they will be furnished with details of the secret tastings. They are taking place in 11 Spanish cities tomorrow (Feb. 27). 

The campaign is by Madrid agency PS21, which has created a film, seen here, around the promotion, in which rival employees arrive anonymously and then sit with "Colonel Sanders" at a secret feast, styled like Da Vinci's "Last Supper" painting. 

La Infame, which contains chicken, cheese, bacon, BBQ salsa and replaces the bread with chicken, is also being promoted by the hashtag #PolloPollo (Chicken Chicken) and will be available until Mar. 22.  It's a version of a menu item that has been launched in other territories; for example, in the U.K. it's known as the Double Down.