Red's stomach muscles squeezed with laughter and he held onto a guard rail to keep from being sent across the room by the exertion.
"What I saw was a woman, Red," I went on.
Red laughed out loud and hung on again. "I could use a babe," he said. Suddenly he jerked. "Who hit me?" he asked. Across his face was a red welt, the shape of a woman's hand.
We called them "manifestations" after that and Red called her his ghost sweetheart, although the slap had convinced him it wasn't a ghost. Red's getting slapped was the first indication that perhaps this thing did have matter of some sort, but its ability to remain invisible made it appear that the matter wasn't the ordinary kind.
Finally I came up with some sort of an answer. It was just a crazy idea and there was no way to prove that I was right. I tried to explain it to Red, who didn't know much about atomic physics, but he seemed to get the idea.
"You see, Red, it could be negative matter," I explained.
"What's that?"
"Well, you know what an electron is, I suppose, a negatively charged sub-atomic particle?"
Red nodded.