An excellent visual explanation by the @Guardian of what happened in Korea. See this chart in particular: a change from aproximately 4 to 6 individuals per square meter changes us from behaving like people to behaving like fluids
https://www.theguardian.com/world/2022/oct/31/how-did-the-seoul-itaewon-halloween-crowd-crush-happen-unfolded-a-visual-guide