They rubbed some sort of pen thing on it, and they took the bills to some machine in a back room. At the time, I figured it was because they thought the bills were fraudulent (I was paying with 100s because my card didn't work).

Maybe the pen thing was only to test if the bills were fraudulent, and then the machine in the back of the store could also do drug tests? Or maybe it was all a lie and they were just bullshitting me.

The benadryl thing was a good read