Markdown insists my String is an Array

gistfile1.rb

# @paragraphs is an Array of Strings - various puts'es confirm this.

@paragraphs.each do |paragraph|
  renderer = HH::LessonParaRenderer.new(container)
  markdown = Redcarpet::Markdown.new(renderer)
  p paragraph # Just checking - it's a String!

  # raises: <TypeError: wrong argument type Array (expected String)>
  markdown.render(paragraph)
end