"'I assume you are fimiliar with Philippa Foots Trolley Problem thought experiment?' ... 'Theres a trolley running out of control down a track.' (23.286) Van Houten uses this reference to explain his daughters death. In this scene Hazel starts to under stand that Van Houten is just a grieving father. It supports her earlier statement about it being worse to have a kid die of cancer then to have died from cancer.