expression, ichidan verb
keep one's wits about one; be on guard; be wary of trickery
Idiomatic expression literally meaning 'to put saliva on one's eyebrows,' from the folk belief that doing so protects against deception. Used to describe staying alert and skeptical.
See also: 眉唾物 (まゆつばもの)
甘い話には眉に唾をつけて聞いたほうがいい。
You should listen to sweet talk with a grain of salt.
He is a cautious person who always keeps his wits about him.