Moebius

The train pulled out of the station.
Carl sat back in the soft seat of his first class compartment, continued reading.

"Excuse me, what's the book about?"
He looked up and faced a girl ... maybe 21 years old.
"It's ... math. A phenomenon called *Moebius Strip*".
"Interesting", she said, "I like the cover."
He showed her the title.
"This", he explained, "is the strip. It has just one infinite surface, got no backside."

"Impossible", she whispered.
A slight tremor gave the train a jolt.