Chapter 56: A Bet?
Next was the spatial lock, in which he would freeze the space from moving around a place. He had nothing to test it on, so he was his own test subject. If it was something like teleportation, he would not have tried it on himself even in this immortal form.
Because some parts of rock would just disappear—he doesn't know where—in failed attempts of teleportation, which scared him to try it on himself even here.
When the rocks travel from point A to point B to reach the distance instantly, they travel through a separate space where the space is much closer. It made him understand the concept of how the portal works, and at the same time how dangerous it was.