Why does glue stretch straighter than string?

So I have some bottles of lemonade and I peeled the labels off both of them, revealing the glue underneath. When these bottles were next to each other the glue stuck. I pulled them apart and it forms into long thin strands like this:

What's more interesting is that when the bottles are pushed back together, the strands remain in tension and if they happen to slacken, they always return to tension over time, eventually becoming very thin and snapping.

This image shows approximately what happens, first (top left) we begin to move the bottles apart, then (top right) we have the thin, straight strands from the photo, then moving the bottles back together we get some slack (bottom left), but the slackness starts to disappear (bottom right) and goes back to tension.

What is it about glue that makes it behave differently from string (which would remain slackened in that well known $y=\cosh(x)$ catenary shape? Why do the strands become extremely thin, eventually snapping? Answers, even if heavy on the maths/fluid dynamics/mechanics are perfectly acceptable.

• Do you need a necessarily quantitative answer ? Commented Jun 12, 2015 at 10:30
• @Gaurav not strictly, although it would be interesting to see some mathematics, or a model of the forces/viscosity at work. Commented Jun 12, 2015 at 10:39