I have a plastic grocery bag, but the top is tied very tightly in a knot like the image below.
I would prefer to not rip open the side of the bag because I would like to reuse it.
I would use a fork if I had one at hand, but I don't usually carry a fork (or anything that could be used as a fork) around with me. The knot is too tight for me to untie it with my fingers. Is there any method or strategy I can use to untie it with only my fingers and without ripping it open?