neck-verse (n.)

some printed Latin text (usually Psalms li.1) "set by the ordinary of a prison before a malefactor claiming benefit of clergy, in order to test his ability to read. If the or his deputy said legit ut clericus (he reads like a clerk or scholar), the malefactor was burned in the hand and set free, thus saving his neck" [Century Dictionary]. See neck (n.) + verse (n.).