During Part 1, you'll get to a point in the story where Mae and her friends find a severed arm on the sidewalk. As the dysfunctional young adult that you are, you'll want to poke it with a stick. When you are in control of the paw and stick, there will be a roach crawling around the arm. This is what you need to squash with the stick for the trophy. Be careful as this part has a soft timer of about a minute and will automatically progress with the story whether you poke it or not.