Siri is pretty funny sometimes. This is one of those times. All you have to do is ask her “What does the fox say?”
Siri will answer back with something like “Chacha-chacha-chacha-chow!”
She has a few more answers, and all of them are based on the popular meme/song. You can listen to it here, but you probably don’t want to. It’s too catchy for anyone’s good, and it will likely stay in your head or give you nightmares (or both).