I think that this is a very unusual story because it has a weird ending and what happens is weird too.
It says that when he put his name and address he noticed that the last two entries were from two to three years ago. Then he remembered them as the missing people in the newspaper headlines.
For some reason almost everything was dead. The Dachshund was dead (preserved and stuffed) and so was the parrot.
And when he sipped his tea, it tasted like bitter almonds. Which is sometimes highly poisonous.
I’m pretty sure that in the end Billy probably dies from the bitter almonds and if he did, the little old lady probably preserved him too. Like how she stuffed the other two. (I think)