Crawl not staying on domain

While running a crawl, I am sometimes getting page results from other domains. The following code:

require 'rubygems'
require 'anemone'
require 'pp'

Anemone.crawl("http://www.ou.edu/") do |a|
  a.on_every_page do |x|
   pp x.url
  end
end

checks multiple other domains and subdomains.