@classmethod
def find_tendril(cls, proto, addr):
    """
        Finds the tendril corresponding to the protocol and address
        tuple.  Returns the Tendril object, or raises KeyError if the
        tendril is not tracked.

        The address tuple is the tuple of the local address and the
        remote address for the tendril.
        """
    proto = proto.lower()
    return cls._tendrils[proto][addr]
