Word processing question

This is a simple question, but I can't figure it out.

When typing in Word Perfect, what causes the words to eat themselves?

Like if I'm typing something, and then go back with my mouse and place the cursor in the previous paragraph and start typing to insert something I missed, the letters I type eat the letters that are already there, and not just expand the paragraph. I was typing alright before, but I did something that is causing my corrections to cannibalize what's already there, and I want to go back to being able to insert stuff without losing what's already there.

Halp!

 

Did you accidently hit the <INSERT> key? Use of this key allows Overwriting ("cannibalize") of text or inserting text - depending upon when <INSERT> key is used.