At the bottom of Word's vertical scroll bar sit three esoteric buttons: one with a picture of two up arrows on it, one with a picture of two down arrows on it, and one in-between them with a picture on it that looks a little like a planet.
These buttons have existed since at least Word 97, yet most people never notice them.
What do these mysterious buttons do?
They're navigation controls. By default, the up arrow and down arrow buttons let you quickly go to the previous or next page of your document, respectively.
The behavior of the arrows can be modified by clicking the little circle button between them. A flyout menu appears which allows you to choose another way to navigate the document.
For instance, you could choose "Browse by Comment" to make the arrows take you between previous and next comments in the document. Or "Browse by Table" will empower the arrows to jump you between tables. You can also choose to navigate between footnotes, endnotes, graphics, sections, edits, and more.
Change the behavior of the navigation arrows
There's one other cool feature built in to these controls. Perform a find in your document (by pressing CTRL+F, or by choosing Find on the Edit menu.)
Now you can close the Find dialog and use the arrows to navigate you between previous and next search results within your document. Notice that the arrows "light up" to show that they're loaded with a search term.
In certain versions, you might even notice the Find dialog box animate up from these controls as it appears, trying to give you a clue that the two features are somehow related. As you close the Find dialog box, you might notice it "minimizing" down into the buttons for the same reason.
Now you know the hidden secret of the mysterious buttons. Franklin W. Dixon would be so proud!