Secret Squirrel
>>7433126
>>7433100
>>7433043
https://www.nsa.gov/Portals/70/documents/about/cryptologic-heritage/historical-figures-publications/publications/cryptologic-quarterly/cryptologic-quarterly-2019-01.pdf?ver=2019-07-31-114255-157
Many species have Identification Friend or Foe (IFF) recognition systems involving visual, olfactory, aural, and other signals. For example, some fireflies evidently differentiate themselves from interlopers by the intervals between, and intensity of, their flashes. Whales, capitalizing on ducting, communicate sonically over distances of hundreds of miles under water. In addition to recognition systems, wherever cooperating groups are involved, communications are used extensively for warning. Beavers do it with their tails, while vocal animals use a variety of barks, roars, and calls; insects use the color red, and, familiarly, squirrels and birds do it with chatter when they detect cats, snakes, or other predators.