It's kind of what I said, that they'd taste test it, but I've seen some eat things known to be toxic like mistletoe
after the first taste. To me, better safe than sorry. I've never heard of anyone using coffee grounds as bedding as someone mentioned. How on earth could anyone gather that many coffee grounds in the first place in an amount to fill a coop? And why would they in the second place? That stuff stains. Doesn't seem prudent. Seems anyone can get some sort of safe, absorbent bedding for their chickens.
Adding: Apparently some company makes bedding from coffee grounds. It's $20 for 35 lbs, no idea if it expands at all. That's twice as much as shavings at $10/bag that expands to 10 cu ft. No idea why these oddball ideas always pop up, no offense intended. Seems bizarre to me and a lot more pricey than regular beddings. I've certainly ever heard of a breeder doing it. Bedding has to be absorbent and non-toxic. Maybe it works fine, but I'll stick with dried pine shavings because I have a 20 x 24 barn to fill. And the aromatic nature could be dangerous for chicks since chickens are very sensitive to aromatic bedding. I live in the south, no one sells anything like that here in the N. GA mountains that I've seen. The weird things I learn...

BUT that was not the original poster's question so carry on, sorry for the interruption.