Hello, What you do depends on your level of concern. I have no way to tell you whether or not he may have swallowed a nail. If you are worried, then you must take your son to the local ER, where they may do an Xray to look for a nail. If anything is visualized, they may need to do a scope procedure to remove it before it scratches / punctures the intestine. If you are worried, please take your child to ER now.