They ran to the door of the cellar, but Toto was afraid, and he ran under the bed.
— Chapter 1 of The Wizard of Oz(Oxford Bookworms Library Stage 1)
In this book, There is no bed that has been mentioned. And I don't know anything about the bed. But as you can see, the definite article "the"is used in front of the word "bed".
To tell the truth, I have questioned about this topic here. People who gave me answers wrote that the definite article "the" implies that there is only one.
There were four walls, a floor and a roof, which made one room;and this room contained a rusty looking cooking stove, a cupboard for the dishes, a table, three or four chairs, and the beds. Uncle Henry and Aunt Em had a big bed in one corner, and Dorothy a little bed in another corner.
— Chapter 1 of The Wonderful Wizard of Oz: 100th Anniversary Edition
In another edition, The inside of the house is described.
There are two beds.
Could you explain me why the definite article is used?