Until 1827, people charged in ordinary criminal courts could claim exemption from some punishments, especially capital punishment, by virtue of ‘benefit of clergy’, or being a professional member of the Church.
In 1305, even minor members of the church were granted 'benefit of clergy'. Defendants could satisfactorily prove their right to 'benefit of clergy' by demonstrating their literacy.
Defendants used to read an appropriate verse from the Bible. This was commonly verse 3 of Psalm 50.
As recitation of this verse was enough to escape hanging (offenders were branded on the thumb, to make sure that they could only claim this benefit once), it was known as the neck-verse.