':param fuzzable_request: A fuzzable_request instance that contains
(among other things) the URL to test.'

def crawl(self, fuzzable_request):

    original_response = self._uri_opener.send_mutant(fuzzable_request)
    original_response_repeat = repeat(original_response)
    mutants = self._generate_mutants(fuzzable_request)
    args = izip(original_response_repeat, mutants)
    self.worker_pool.map_multi_args(self._check_existance, args)
