Mason said, “I’ll tell you one other significant thing. Every word contains either the letter a or the letter b.”
“I don’t see that that’s as important as the frequency with which the letter c occurs.”
“Perhaps not, unless we also consider positions. Every word has either a or b in it, but neither a nor b appears at the first of the word or at the ending. They’re always either the second or third letter from the end of the word.”
There followed an interval while she checked his conclusions, then nodded again.
Mason said, “That empty can is significant in a good many ways. I’m wondering whether Tragg has overlooked some of those things, or is just sitting tight and awaiting developments.”
“What, for instance?” Della asked.
“That can conveyed a message to some person,” Mason said. “That means two persons were concerned in the crime. That, in turn, means that the someone who put the can there must have had easy access to the basement. It also means that the person for whom the message was intended must have had easy access to the basement. Yet it also means that those two persons didn’t have access to each other. ”
“I don’t get you,” Della Street said.
“It’s simple,” Mason pointed out. “If the two persons could have met and talked with each other, there would have been no necessity for going to all that elaborate trouble of scratching a message in the top of the can, sealing the can, and placing it in the cellar.”
“Yes. That’s true.”