Snickers, Maltesers, Minstrels and Twix would no longer be suitable for vegetarians because of the introduction of rennet, a chemical sourced from calves' stomachs used in the production of whey. The rabbinical authorities declared that the products remained kosher for Jewish consumption. The decision was condemned by several groups, with the Vegetarian Society stating that "at a time when more and more consumers are concerned about the provenance of their food, Mars' decision to use non-vegetarian whey is a backward step". Mars later abandoned these plans, stating that it became "very clear, very quickly" that it had made a mistake. Economics It has been observed on several occasions that the price of a Mars bar correlates fairly accurately with the change in value of the pound sterling since World War II, much in the way that the Big Mac Index has proven to be a good indicator of the actual relative purchasing power of world currencies. Popular culture Northern Irish pop-punk band The Undertones wrote and recorded a song called "Mars Bars", released as a B-side in 1979. 1960s Liverpool band Gerry and the Pacemakers were originally known as Gerry Marsden and the Mars Bars before changing their name due to the objection of Mars, Incorporated. The 1990 Newbery Medal winning novel Maniac Magee features a character named "Mars Bar" Thompson, his nickname given for his recognition of eating Mars Bars (his real first name is never revealed). References External links The Visible Mars bar project, which shows the difference between US and UK Mars bars. Site with cross-sections of both the original US and Canadian Mars bars Slough History Online Television commercial for original US Mars bar showing ingredients Products introduced in 1932 British confectionery Chocolate bars Kosher food Mars confectionery brands Slough Brand name confectionery