Scars
A very deep scar can become numb beyond its edges. A grafted piece of skin loses sensation. If they're touched lightly enough then nothing is felt; fingers jumping from bank to bank. There might be a far-off prickle, and pressure will be felt by the muscles beneath, but ultimately it is a hole - a dry ravine, a ragged canyon, or something man-made and deliberate.
A body is meant to be closed, we are all contained within walls. But any wall can be damaged to the point that it will never fully seal. And a window can be curtained, but it will never be a wall.