Anybody who hears this chalk used on blackboard has their doubts removed about particular people. In this case, it's necessary for Keroro to write the names of these people in order for the chalk to work properly. Keroro made use of the chalk at that time when "invading" Fuyuki Hinata and Momoka Nishizawa's class in an attempt to learn more about Pekopon youths while disguised as a teacher. While the Acceptance Chalk can double as a regular chalk stick, Keroro needs to use it three times in order to erase suspicion about himself, Giroro and Tamama, who are also in the classroom. Fuyuki and Momoka are not immune; they covered their ears to protect themselves from falling into its hypnotic resonance. Oddly enough, Chiruyo Tsukigami seems to be immune to the chalk's effects though this could be due to her journalistic skepticism or because of her glasses (it seems you need to both see and hear the chalk for it to work so she might have removed her glasses when Keroro started writing).