On page 34 of the PDF in the first sentence of the paragraph following the BookInStock initialize method example there is either an extraneous “a” or a missing noun following the word “special.”
The text reads:
“The initialize method is a special in Ruby programs.”
case correction_option
when "extraneous 'a'"
"The initialize method is special in Ruby programs."
when "missing noun"
"The initialize method is a special #{missing_noun} in Ruby programs."
end