I found this Toy Box for birds. I appears enough to make at least 3 or more toys for me birdies but I'm not sure what kind of string I should use, that's safe.
Every one has jogging pants or hoodies, and those irriating strings that love to come part way out and you can never get them to go back in Or they come all the way out...
So I use them for the birds toys They are 100% cotton and have not yet frayed on me (with the exception of the 2 ends I tie the not in) and most of them have had the same string for a little over a year
I also use what I call Butchers Twine - its cotton string (really looks like thick thread in a way) and it comes on a Cardboard tube like toilet paper/ paper towels do.
Also They say Hemp is safe (still confused about that one but i'll keep that argument to myself because I know exactly where hemp comes from LOL)