irb(main):002:0> moo = [[1,2,3,4,5,6,7]]
=> [[1, 2, 3, 4, 5, 6, 7]]
irb(main):003:0> moo.clone.each { |x| puts x.shift }
1
=> [[2, 3, 4, 5, 6, 7]]
irb(main):004:0> moo
=> [[2, 3, 4, 5, 6, 7]]
irb(main):005:0> moo.dup.each { |x| puts x.shift }
2
=> [[3, 4, 5, 6, 7]]
irb(main):006:0> moo
=> [[3, 4, 5, 6, 7]]
irb(main):007:0>