On some aircraft, such as a 767-400, those buttons are supposed be used in a choreographical sequence to create a song.

For example, this one is from the Wizard of Oz:

ding - ding - ding ding ding ding - ding ding ding - ding ding ding ding - ding ding - ding ding ding ding ding ding ... (repeat)

There are little lights in the passenger service unit that illuminate in sequence with the "dings", creating a nice little music 'n light show on board the aircraft.

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