To me this is the quintessential sound of a summer night. We’ve always had katydids in our neighborhood; and yes, they really do sound like they’re saying “Katy did, Katy didn’t.” By far the world’s longest-running stupid argument.
Depending on the species, they can make a lot of different sounds, and some of the tropical species are as big as your hand. The ones around here are about the size of your thumb. Like the one that tried to climb up Patty’s pants-leg (still laughing over the ensuing war dance…).