The gunk processor initiates the broadcast of a message. The program continues while the message is transmitted. The message may be any scheme object, but it is best to stick to realistic data structures like lists, vectors, strings, numbers and symbols.
At the completion of the transmission, if the message was not corrupted, the receiving processor's primitive-message-event is signalled with the message. If the message was corrupted then the receiving processor might detect the collision (signalling 'collision) or fail to detect the message completely (not signalling anything).