array = %w{bob loves alice}
array.collect { |x| x.capitalize }

array.collect_reverse { |x| x.capitalize }

["Alice", "Loves", "Bob"]

Error! (Exception?) Here's stdout:
NoMethodError: undefined method `collect_reverse' for ["bob", "loves", "alice"]:Array
	from (irb):3

require 'enumerator'
reversed_array = array.to_enum(:reverse_each)
reversed_array.collect { |x| x.capitalize }

reversed_array.each_with_index do |x, i|
  puts %{#{i}=>"#{x}"}
end

0=>"alice"
1=>"loves"
2=>"bob"

0=>"alice"
1=>"loves"
2=>"bob"

reversed_array[0]

NoMethodError: undefined method `[]' for #<Enumerable::Enumerator:0xb7c2cc8c>

Error! (Exception?) Here's stdout:
NoMethodError: undefined method `[]' for #<Enumerable::Enumerator:0xb7c2c854>
	from (irb):10

array_with_index = array.enum_with_index
array_with_index.each do |x, i|
  puts %{#{i}=>"#{x}"}
end

0=>"bob"
1=>"loves"
2=>"alice"

0=>"bob"
1=>"loves"
2=>"alice"

array_with_index.each_with_index do |x, i|
  puts %{#{i}=>#{x.inspect}}
end

0=>["bob", 0]
1=>["loves", 1]
2=>["alice", 2]

0=>["bob", 0]
1=>["loves", 1]
2=>["alice", 2]

sentence = %w{Well, now I've seen everything!}
two_word_window = sentence.to_enum(:each_cons, 2)
two_word_window.each { |x| puts x.inspect }

["Well,", "now"]
["now", "I've"]
["I've", "seen"]
["seen", "everything!"]

["Well,", "now"]
["now", "I've"]
["I've", "seen"]
["seen", "everything!"]

two_words_at_a_time = sentence.to_enum(:each_slice, 2)
two_words_at_a_time.each { |x| puts x.inspect }

["Well,", "now"]
["I've", "seen"]
["everything!"]

["Well,", "now"]
["I've", "seen"]
["everything!"]