Rowling’s tweets may not seem troublesome or hateful to people who don’t have a good grasp on the language of “gender critical feminism,” which is a movement that has grown to prominence in the UK, where Rowling lives. But her statements are insidious; they remove trans people’s ability to define their gender for themselves, instead using genitalia, chromosomes, and assigned sex at birth (known as biological essentialism) as the only way to determine someone’s gender. While Rowling’s initial tweet invalidated the identity of AFAB (assigned female at birth) trans people, “gender critical feminists” are most concerned with trans women, believing them to be men infiltrating women’s spaces and threatening cis women’s safety (despite no evidence to support this, and the fact that trans women are more likely to be the victim of an assault in those spaces than the perpetrator).