Give a graph and consider two simple random walks on it.We say that the two walks collide infinite many times if their space-time trajectories intersect infinite many times.It is interesting that Comb(Z) is a graph on which two simple random walks almost surely collide finitely many times, while the expected number of collisions is infinite.In this short talk, we shall show some sufficient condition for infinite collisions of simple random walks on a subgraph of Comb(Z).