If you ever need to cut through some rope or string and you don't have any tools around, you can use the strand to cut through itself with some friction and a little elbow grease.
YouTuber DaveHax explains in this video how to set yourself up for blade-less rope cutting. Make a mark on the rope or string of where you want the cut to be, then lay it on the ground so you can hold it in place with your feet. Make sure your mark is in the middle, grab whatever slack you have, string it under the mark, and pull until it's taut. Now start "sawing" as demonstrated. This works well on nylon rope and string, but it's possible on other types if the strand isn't too thick. Tools are much more efficient, but now you're prepared for any circumstance.
How to Cut Rope in an Emergency [YouTube]