I found a 1x1 round plate with one end of a "string with end studs" stuck on top of it surprisingly difficult to get apart with my bare hands, without ripping the string off. [![string with end-studs][1]][1]  

If you have 2 brick separators available (one above and one below), or a plate and a brick separator it is easy as you can lock each piece, but with bare hands it is completely impossible. 

  [1]: https://i.sstatic.net/NEy2A.png