Mysterious

From "The phonetics-phonology interface" by John Kingston in The Cambridge Handbook of Phonology (2007, Paul de Lacy ed.)

The development of tone from an earlier contrast in laryngeal articulations of an adjacent consonant is an extremely common sound change (Hombert, Ohala, & Ewan, 1979), particularly in the language families of East and Southeast Asia.

There are two assertions in this quote, and I think one of them is far more mysterious than the other. It's interesting to me how easily they can be mixed in a single breath.