Not ignored!

  doesNotUnderstand: aMessage

  "Handle the fact that there was an attempt to send the given message to the receiver but the receiver does not understand this message (typically sent from the machine when a message is sent to the receiver and no method is defined for that selector).

  Raise the MessageNotUnderstood signal.  If it is caught, answer the result supplied by the exception handler.  If it is not caught, answer the result of resending the message within a guard for infinite recursion. This allows, for example, the programmer to implement the method and continue."