Now, by just looking at this, your first thought is probably going to be “wtf does this video have to do with 3D printing?”. I’ll tell you what.
This is the same thing that happens to our filament in the nozzles as it’s extruded. This is what makes simply combining filament so difficult. However, this also can also be utilized for some very pretty effects as seen in @Richard_Horne 's blog: http://richrap.blogspot.co.uk/2012/08/3-way-quick-fit-extruder-and-colour.html