String and a blue tit

Outside and near to my kitchen window are three plastic sacks of soil into which I am planting beans this year.
Broad beans are already growing well there.
To accommodate the climbing beans (Climbing French and Blue Lake) I have constructed a bamboo frame, giving each plant either a bamboo or a vertical strand of green, garden string up which to climb.
Looking out of the window one early morning in late April, I saw a blue tit struggling and swinging round at the top of one of these strings.
I witnessed its distress for a short time before planning to go outside and free the poor fellow.
Then I noticed that it was sliding downward. Perhaps the string had become wound around its leg.
Then, apparently still struggling, it fell lower still.
It was about to be saved when I noticed that the bird was not attached to the string at all, but holding on to it.
Lower it went, pecking at the string all the while.
By the time the blue tit had reached the bottom of the string it had harvested a beakful of short green strands, made of jute, sisal, hemp, or whatever garden string is made from.
Then off it flew to add decoration to its nest.