What is the foreshadowing in "The Landlady"?

The reader is kept in Billy's point of view and picks up clues with the viewpoint character but attaches more significance to them. The first would be the cheapness of the rent, which is only five shillings and sixpence a night and includes breakfast the next morning. There were twenty shillings to a pound in those pre-decimalization days. A pound was worth about five American dollars. There were twelve pennies in a shilling. So a shilling was worth about twenty-five American cents and sixpence, or half a shilling, would be worth  twelve-and-a-half cents. Five and sixpence would be equivalent to $1.37. And this is a resort town!

The next bit of foreshadowing comes right after Billy enters.

There were no other hats or coats in the hall. There were no umbrellas, no walking sticks--nothing.

The landlady explains that she is

". . . just a teeny-weeny bit choosy and particular--if you see what I mean. . . . But I'm always ready. . . . just on the off chance that an acceptable young gentleman will come along. . . . Like you," she added, and her blue eyes traveled slowly all the way down the length of Billy's body, to his feet, and then up again."

At that point Billy should decide to get out of there.

The next foreshadowing comes when he sees the names and addresses of Christopher Mulholland and Gregory W. Temple in the guest book. Both names seem familiar, but he can't remember why. Again the landlady shows her interest in handsome young men.

"Oh no, I don't think they were famous. But they were incredibly handsome, both of them. . . .They were tall and young and handsome, my dear, just exactly like you."

Billy should at least be getting the idea that he might find her in his bed in the middle of the night. The reader is getting very suspicious of this woman but doesn't yet begin to suspect that she is a real lunatic who kills her guests. After all, this is a homey bed-and-breakfast establishment in the stodgy town of Bath.

The reader doesn't see anything suspicious about the landlady serving tea because this seems so characteristic of such a woman. The author has the reader suspecting that something may happen  after Billy has gone to bed. But here it is happening just a few minutes after Billy has signed the guest book. The tea actually seems like the opposite of foreshadowing.

Then the clues and foreshadowing get heavier and more ominous. Billy sips his tea and detects a strange smell. When she mentions that Mr. Mulholland "was a great one for his tea," Billy says, "I suppose he left fairly recently."

"Left?" she said, arching her brows. "But my dear boy, he never left. He's still here. Mr. Temple is also here. They're on the fourth floor, both of them together."

This is shocking. The reader feels certain she has murdered both young men. And then she says of Mr. Temple:

"There wasn't a blemish on his body. . . . His skin was just like a baby's?"

How could she know that?

At about this time Billy discovers that the parrot is not alive but stuffed. Then he realizes that the dachshund is also the work of a skilled taxidermist.

The tea tasted faintly of bitter almonds, and he didn't much care for it.

Now the reader realizes that it is too late for escape. Billy has drunk a cup of tea loaded with arsenic, and he is going to be the landlady's next victim. He asks if there haven't been any guests other than Temple and Mulholland in the last two or three years, and the story ends ominously with:

"No, my dear," she said. "Only you."