Ink

tap the right ink. the rule will change.

a press prints colour names, mostly in the wrong inks: tap the tin the word names, then, when the rule flips, the tin of the ink it is printed in, before the ink dries. Three spoiled slips and the run is over

Tap the ink the word names, until the rule turns over: then tap the ink it is printed in. It flips again and again, faster, and the tins change places each time. The ink rule is much harder on the same words, because you read them before you can stop yourself. This is the Stroop effect (J. R. Stroop, 1935), and the proof at the end is your own two average times.

Concepts: attention, perception, language, color.

An interactive you play with one thumb, on Wundr.