My BiL was a dentist. He had a large group of friends over for a cookout and pool party. He, jokingly, made everyone take a tablet when they arrived.
They were dental disclosing tablets used to show areas missed by cleaning treatments.
They also turned the urine red when someone peed in the pool.
About once a year Uncle Sam would line us up, everyone gets a tablet and must CHEW it up.
A team of ‘trained’ inspectors would check for the dreaded plaque.
Always a few would swallow the tablet, so they could impress their buddies, with technicolor pee!