Don't assume - USE A MAGNIFYING GLASS!
We had this happen and it appeared that the entire piece of string was removed but luckily my son who was helping me has "bionic closeup vision" and could see a bit still wrapped around the tongue that I couldn't see - with the magnifying glass. 
This was bad - the tongue was black. I was sure it was going to fall off. Much to our surprise, the tongue pinked up almost immediately after the little bit left over was removed and the chicken recovered.
So - just to be safe - give a double check with a bright light and magnifying glass. Their tongue has a strange groove that string can hide under.