Finishing "squirt"???

I was at a local eatery last night sitting at the counter, watching the crew cook, plate, and finish the dishes. I noticed for just about every protean there was a bottle of something, usually green, that the squirted on the protean before it went out. It looked too watery for oil but I'm not sure what it was. Also noticed in the movie Chef that Chef Carl (Jon Favreau) is plating what looks like a squab and he finishes with a little squirt of something. So general question, what kinds of things would one use for this? I assume it gives the dish a little extra flavor, makes it look nice and moist, etc. Thanks for any ideas!