That is a very good tutorial.
Everything is done in stages.
Eating salad. You will need an animated sprite.
Basically animation frame 1 will be whole salad. frame 2 will be slightly eaten salad etc etc etc.
And instead of worm overlapping salad and destroying it. It will cycles through the frames.
All tutorials teach the principles, you've just got to mold them into what you want to do. This I'm afraid is trail and error, and there are various ways to accomplish the same thing.
There are no right answers, just many ways to do the same thing.