This People I (Mostly) Admire podcast episode introduced me to the concept of mirror bacteria (or mirror life) which is the idea that biology uses molecules of a specific chirality, i.e. molecular formations that are either right-handed or left-handed.  The same chemical can exist in either form, but all biology tends to use molecules of a specific handedness, e.g. proteins are exclusively composed of left-handed amino acids.  There's a scary idea out there that if left-handed bacteria suddenly evolved or were created in a lab, the human immune system would be unable to defend itself because it evolved to recognize right-handed bacteria only. #science