In traditional Freemasonry, obtaining the first three “degrees” requires passing progressively more detailed cross-examinations about the tenets and rules of Freemasonry. For the third and most important degree (master mason) it is particularly detailed and lengthy.

As Masonry has been traditionally popular in law-enforcement agencies, “give him the third degree” became an “in” reference to a particularly gruelling police questioning.

David Norris, High Wycombe, Buckinghamshire

During the Spanish Inquisition, the first degree was describing the instruments of torture to be used; the second degree was showing the instruments and the third degree was using the instruments.

Terry Leyshon, Coelbren, Powys

Why, among actors, is it unlucky to say “Macbeth”?

Shakespeare, in an attempt to please King James I, an authority on demonology, cast caution aside and reproduced a 17th-century black-magic ritual (“Round about the cauldron go;/In the poison’d entrails throw . . .”, etc). Without changing an ingredient, Shakespeare provided his audience with step-by-step instructions in the art of spell casting. The ritual’s practitioners were not amused by this detailed public exposure of their witchcraft, and it is said that as punishment they cast an everlasting spell on the play, turning it into the most ill-starred of all theatrical productions.

There have been several deaths and injuries during the performance of Macbeth, including an instance in 1672 when the actor playing Duncan was killed by a fake dagger that turned out to be a little more realistic than hoped and a riot in a New York theatre in 1849 that resulted in 31 deaths..

Charlotte Longstaff, Marlow, Buckinghamshire

When someone is knowledgeable about a subject, why do they “know their onions?”

I believed for many years that the reference was to the late lexicographer, C. T. Onions, a compiler of the Oxford English Dictionary, the definitive work on our language. He also wrote the Oxford Dictionary of English Etymology. Onions died in 1965.

I have, however, seen suggestions that the expression may have been in use earlier..

G. M. Beresford Hartwell, Wallington, Surrey