Take your finger and feel the tip of your tongue from left to right and back.
Note how your brain senses it.
Now flip your tongue upside down and take your finger and feel the tip of your tongue again.
Can you feel any difference?
If you can, you're doing it wrong.
This happens because your brain is receiving conflicting feedback from the position of your finger, and the feeling of your tongue. Also, the brain did not consider the possibility of your tongue being upside down, and so it overrides the actual feeling and relays them to how the brain thinks it should be.
Another classic example is viewing the same lip reading of the sound "Buh". If the mouth is dubbed with "Buh", the brain reflects it to where the lips look like they are saying "Buh", however if the sound "Vuh" is dubbed over, the brain alters what you are seeing to match the lip reading of "Vuh"