Cockroach Clusters are sweets made of cockroaches, shaped like peanuts. They are sold at Honeydukes in Hogsmeade. Ron Weasley once thought he could fool Fred into eating some if he told him they were peanuts. Once, when Harry Potter was trying to enter Professor Dumbledore's office, he was able to guess the password, which was "Cockroach Clusters".
Behind the Scences
- In the real world, there are actual Cockroach Clusters candies, which are sold as novelties. The website Candy Addict rated them number seven of the "10 grossest candies." 
- Cockroach clusters may be a reference to the confection referred to in the Monty Python sketch, "Crunchy Frog". The titular Chocolate Frog sweet, however, is not; a small frog-shaped chocolate is a common English confection.