He wrapped himself in a blanket, chattering his teeth and saying 'Brrrrrr it's so cold outside!'

Brrrrrr 是英语中用来模拟寒冷时牙齿打颤或身体发抖的声音拟声词，通常表示"非常冷"的感觉。这种拟声词没有实际词汇含义，纯粹用于模仿声音效果。