The day after Field Day, Ennis finally has a batch of anti-mal concealer that doesn't separate, curdle, turn blue, cause a rash when tested on the shell of a volunteer's ear, or totally fail as makeup.

The question is whether she got it to actually work as magic.

Isla informs her that she needs a control group and to do a science experiment. They kick the question of whether that's affordable, manawise, to the seniors, and Eleanor okays it. Ennis whips up a matching batch of non-magical concealer, and some pigment concentrates to make it match anyone's skin tone because walking around with "concealer" that's six shades too light is a good way to expect it not to work.

So the day after that, Poppy (among others, but it's mostly Poppy) puts out the word that Ennis is giving out anti-mal concealer (intended for any small injury - acne, hangnails, pinkeye, little mal bites, papercuts - that might normally smell tasty to mals) and also a placebo. Signing up to be randomly given a dollop of one or the other randomly (without knowing which) is, conditional on your agreement to report your results and your possession of a relevant blemish, free.