I think it’s A because I assume a portal stitches two points in space to each other.
So if I have a surface A and B with a portal ‘]’ in the middle A0 A1 ] A2 A3. B0 B1 [ B2 B3
A portal creates a new surface
A0 A1 ][ B2 B3
And if you move the portal the new surface changes.
A0 A1 A2 ][ B3
Speed is distance over time. When a portal moves the object that passed through the portal stays stationary. Let’s say I am standing on B2. When the portal advances I find myself standing on A2 , have i moved? No the environment has changed but i am still in the same relative position with respect to the portal surface. No distance travelled so no speed.
Non horns story time …
A long time ago I was but a young lad living in eastern Europe and I use to watch this cartoon. The actual content of this cartoon are lost to the ravages of my memory but a few things stood out, the main character had a flying board and the opening sequence was him flying through these hallways that were broken into geometric shapes and there was a big face that he flew towards.
Sometime later especially during university it became a recurring niggling idea. Did it exist or was it some dream or fantasy? I’d get enthused once in a while and try searching the depths of the net for it with no luck.
It wasn’t until I had graduated and was working, close to 20 years after the fact that I found it ! The name of this show is now imprinted on my brain.