If you make a mistake in your knitting and don't notice it for several rows, the best course of action for fixing it is to remove the work from the needle and simply rip out the rows you have completed since you made the mistake.
This process is known as frogging because you have to just "rip it" and move on.
It's not much fun to have to frog your projects, but you'll be glad you did rather than leaving in a mistake you could have fixed.
Frogging is also the term used when you rip out a whole project and start over, either because you were knitting the wrong size, decided you didn't like the pattern, or for some other reason.


