"Incoming message from the Big Giant Head." is a catchphrase used by Harry when his transmitter function override his normal function.
When Harry receives a message, which is usually come from either The Big Giant Head or his office and with out prior warning, he is completely taken over. The first signs are always physical - he immediately shudders violently, garbles incoherently, then adopts a stance with bent knees and upraised arms, palms forward. Messages always begin "Incoming message from the Big Giant Head!" or "Transmission incoming from the Big Giant Head!". The voice used for the messages are in a more robotic voice than Harry normally uses. The messages end with Harry saying "Resume normal functions in three ... two ... one ...", or later "transmission ending in three ... two ... one ..." after which Harry will normally sneeze or belch and, as he is unaware of what has happened, will comment "So... What'd I miss?!"