This is one crazy illusion! Scientist Lisa DeBruine posted a GIF that was made by @IAmHappyToast on Twitter and asked users what they thought they heard.
The gif isn't making any noise, but a vast majority of users are perceiving that it's making a thud.
What do you think? It seems like no one knows for sure why this is happening. Just the brain playing a trick on you...
(H/T: The Chive)