The beginning of Act 1 Scene 1 of Romeo and Juliet by William Shakespeare is intended to give a concrete example of the extreme nature of the feud between the Capulet and Montague families in Verona, showing that it involves not just the families and their friends but also the servants, and has progressed to such an extreme that it even causes civil unrest and riots.
Sampson and Gregory, two servants of the house of Capulet are walking down the street, armed with swords and bucklers. Their conversation indicates that they are looking forward to a brawl with any associates of the Montague family they encounter.
Sampson says that he will bite his thumb (the equivalent of a modern extended middle finger) at the Montagues if they encounter any, and when they encounter two Montague servants, he does so. A brief verbal argument ensues and then both pairs of servants draw their swords.