What you Need
What to do
Get a small drop of spit between your thumb and forefinger.
Slowly pull your finger and thumb apart forming a lovely string of spit about 10-15mm long.
Watch the string for 10-15 seconds and see if anything interesting happens.
If you want another go, and it doesn't work, try some fresh spit.
What may happen
You should find that the string of spit, slowly turns into a string of droplets, held together by a thin line of spit.
Why does it happen?
Spit is mostly water, but it doesn't quite behave like water, it is a little bit more viscous than water and it is much better at lubricating than water. This is because it is full of long thin protein molecules, which tangle with one another making the liquid slightly thicker, which helps it lubricate.
When you stretch out the liquid you will also tend to stretch out the molecules a bit.
The rest of the spit is water, and water has a property called surface tension, there is a constant force attempting to minimise the surface area of the water.
If the surface is curved this acts to increase the pressure in the water, the more curved the water is the higher the pressure, This means that if part of the string of spit is slightly narrower than another, its pressure will be slightly higher, so spit will move from the narrower section to the wider one. This means that the spit slowly forms the beads.
The protein polymers are stretched in between the droplets and tangle up with one and other, effectively creating a string like structure between the beads.