It's a very interesting article. If you wouldn't mind, I'd like to amuse my geeky side and add some info to it. Grass and hay, as important as they are, aren't the only phytolith-rich foods for guinea pigs. Many plant species have some form of phytolith protection. My own pigs occasionally have dried nettle and fresh mulberry tree branches - although I have to admit I feed them because the pigs enjoy the taste, not for the phytoliths, but I guess they do help getting their teeth worn down.