If they meant nails like fingernails I'm completely lost. But I used to with regular nails for the metal taste. I almost died as a kid because I used to suck on small nails and screws. Surprisingly that's not what stopped me from sucking on them. It was because i unconsciously bit down one once and that shit hurt. Used to do coins too but when I found out what germs were and how many germs are on money I stopped immediately.

I cut my nails and chew it and spit it out later

please elaborate

This is uncalled for, to say the least. The very idea of someone chewing on (clipped) nails was problematic enough