You need to have all of your letters on the board forming multiple words for this one. Here's an example of mine where I made Suets, Faces, Foe, and El:
If you get six letters out and just can't seem to think of anything for the last letter, just start putting it in random places. You'd be surprised just how many strange two-letter words there are.
If you use all seven letters to make just a single word across the board, you will instead get