The leaves in romaine hearts are like little canoes. You can use them to hold lots of things. Veggies, salsa, fruit salad, chicken salad, etc. It's a quick and easy way to make a pretty presentation and you can eat the bowl!
The little crabs are punched out of carrot slices. I have a bunch of really intricate food punches that I found in Hong Kong many years ago, but you can find them in any good China town. Got to have a little fun with food too