> It never occurred to anyone to inject a radioactive tracer... I'm going to post the relevent xkcd comic, although I fear you failed to meet this standard: ht

> It never occurred to anyone to inject a radioactive tracer... I'm going to post the relevent xkcd comic, although I fear you failed to meet this standard: https://www.xkcd.com/793/ https://www.xkcd.com/793/