Method chaining can still _be_ magical, and not have to _look_ like magic.

commaize.rb

number = 1234567

# Chaining methods more than once-ish is confusing; the developer has to keep
# in mind wtf is going on:
number.to_s.reverse.split(//).each_slice(3).map(&:join).join(',').reverse

# Commenting the state of each chain helps:
number.to_s.      # String,                                 e.g. "1234567"
  reverse.        # reverse it,                             e.g. "7654321"
  split(//).      # split on every character,               e.g. ["7", "6", "5", "4", "3", "2", "1"]
  each_slice(3).  # Enumerator for every 3 elements, effectively [["7", "6", "5"], ["4", "3", "2"], ["1"]]
  map(&:join).    # map each element, x, to x.join(),       e.g. ["765", "432", "1"]
  join(',').      # join those elements with commas,        e.g. "765,432,1"
  reverse         # re-reverse,                             e.g. "1,234,567"