Very interesting @scienceblocks
My dog eats very often grass, but she doesn't touches leaves. I've heard many different things. The vet said it was very bad and she had stomach problems, again someone said it was deficiency symptoms, still someone else said it was a tick and again others said it was about the consumption of dietary fiber.
When she eats grass to puke, then she will eat old and fresh grass (just the kind with the long leaves). She starts puking really fast with this. I also would say she eats more grass she changes the fur (Summer/Winter and Winter/Summer).
But she can also eat fresh young grass in masses without puking. Maybe the fresh grass has a special taste that she likes very much.
I can't really explain it either.