def sense(self):
haystack = bitstrings.BitString.random(self.input_size)<EOL>self.needle_value = haystack[self.needle_index]<EOL>return haystack<EOL>
Return a situation, encoded as a bit string, which represents
        the observable state of the environment.

        Usage:
            situation = scenario.sense()
            assert isinstance(situation, BitString)

        Arguments: None
        Return:
            The current situation.