i did not understand the joke

"why was 6 afraid of 7? because 7 *ATE* 9" until i was WELLLLLL into my 20s..... until one day i was scrolling on social media and saw THIS specific image LMAO.... i always thought people were saying "because 7, 8, 9" like they were a GANG or something ???? i cant even explain to you the clarity that came over me when i first saw this image LMAOOOOO