look it crackles and pops

crackle_pop.rb

#! /usr/bin/env ruby

sum  = ->(top, bottom) { top.zip(bottom).map{|array| array.inject('', :+) } }
mask = ->(top, bottom) { top.zip(bottom).map{|mask_layer, bottom_layer| mask_layer.empty? ? bottom_layer : mask_layer  } }

list         = (1..100).to_a
crackles     = list.map{|num| (num % 3) == 0 ? 'Crackle' : '' }
pops         = list.map{|num| (num % 5) == 0 ? 'Pop' : '' }

# ['', '', 'Crackle', '', ''   , ...]
#             SUM
# ['', '', ''       , '', 'Pop', ...]
#              ||
# ['', '', 'Crackle', '', 'Pop', ...]
crackle_pops = sum[crackles, pops]

# ['', '', 'Crackle', '', 'Pop', ...]
#             MASK
# [1 , 2 ,  3       , 4 , 5    , ...]
#              ||
# [1 , 2 , 'Crackle', 4 , 'Pop', ...]
result       = mask[crackle_pops, list]

puts result.join(', ')

# `ruby crackle_pop.rb test` to run
if ARGV.size == 1 && ARGV.first == 'test'
  require 'test/unit'
  extend Test::Unit::Assertions

  assert_equal 1,           result[0]
  assert_equal 'Crackle',   result[2]
  assert_equal 'Pop',       result[4]
  assert_equal 'CracklePop',result[14]
end