There are a selection of clips to listen to. Each time you reply to Alexa you can either ask for a new illusion one or repeat the one you have just heard. A muffled clip will play 2 times. Try as you might you should not be able to make out what is being said. The original clip will then play, after which the muffled one will play again. Once you hear the muffled clip after hearing the original one you should be able to make out what is being said. If you ask for the same clip again you should be able to make out all the muffled clips.
This illusion plays on the way your brain interprets the world. Your brain is always trying to make sense of all of your senses. Without hearing the original sound your brain has no idea what is being said. But once your brain knows what to expect and has heard the sentance, it will try to use that knowledge to understand the muffled audio.
I hope you enjoy these clips. The library of clips will continue to grow so keep checking back.