The idiomatic expression "kind of chemistry" is used to describe a certain type or quality of interaction between two people, often indicating that there is an unspoken connection or attraction between them. It can also refer to a natural compatibility or rapport that exists between individuals who work together or spend time with each other. In essence, the phrase suggests that there is something special or unique about the relationship between these individuals, even if it's difficult to put into words exactly what that "something" is.