After watching the horror movie, he shivered and said, 'Brrrrr, that was so scary!'

Brrrrr 是一个拟声词，模仿人因为寒冷或恐惧而发抖时发出的声音，通常用来表达"冷"或"害怕"的感觉。在这个句子里，它用来强调说话者因为恐怖电影而感到的恐惧。