Focus on the pronunciation of sleeper
English definition of “sleeper”
/ˈsliːpər/ noun [C] (also sleeper hit) MARKETING
› a product, film, book, etc. that becomes a sudden success, after a period of not being successful at all: The movie cost only $400,000 to make, and then blew up into a $39 million sleeper. Her book has been the big sleeper hit of the literary scene.