Sessions of the House of Commons have sometimes been disrupted by angry protesters throwing objects into the chamber from the galleries—items thrown include leaflets, manure, flour, and a canister of chlorobenzylidene malonitrile (tear gas). Even members have been known to disturb proceedings of the house. For instance, in 1976, Conservative MP Michael Heseltine seized and brandished the mace of the house during a heated debate. However, perhaps the most famous disruption of the House of Commons was caused by Charles I, who entered the Commons Chamber in 1642 with an armed force to arrest five members for high treason. This action was deemed a breach of the privilege of the house, and has given rise to the tradition that the monarch does not set foot in the House of Commons.