When my son was 8 or 9, he hurt his toe riding his scooter and the toenail turned bright green before it eventually fell off. We kept it in a zip lock bag for a long time.
I've lost several toe nails over the years due to carelessness while working outside in sandals or barefoot; and yes, they do generally turn a bruised color first. Haven't kept any of them for memories sake, though; that seems a little
I suppose that could happen to a chicken too, but I'd watch it closely. A toe nail falls off, a toe damaged to that extent could lead to infection...if that's the problem