Intransitive verb and Godan verb
はずむ
彼との会話がこんなに弾むなんて、思ってもみなかったわ。
I never expected such a lively conversation between the two of us.
Weird that this kanji means bullet but the verb vocab version means to bounce. Just imagine someone shooting a bullet. What does it do when it hits the right materials? It's going to bounce.
If you're going to bounce something off that wall, it has (はず) to be made of rubber, otherwise it will just go right through. It has to.