“[It] is not the most intuitive of phrases. Although people’s pants do sometimes catch on fire, this correlates more with carrying around accidentally explosive materials than it does with truthfulness. Meanwhile, the vast majority of liars make it through life unscathed by this particular fashion catastrophe. The mystery of the phrase’s origins is compounded by the fact that several of its more popularly reported etymologies are, in fact, lies.” Cara Giaimo gets to the bottom of the matter.