In Game 1 of the Book of Why, represented by the causal diagram X rightarrow A rightarrow Y and A rightarrow B, there are no confounders between $X$ and $Y$. The variable $B$ is associated with $X$ because it is in the X rightarrow A rightarrow B chain, and it is associated with $Y$ because of the open path B leftarrow A rightarrow Y. Although $B$ is correlated with both $X$ and $Y$ and is not on the causal path between them (thus passing the classical epidemiological definition of a confounder), $B$ is not a confounder because it does not causally influence $X$.