Synovial fluid

Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency ("synovial" partially derives from ovum, Latin for egg), the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.

http://en.wikipedia.org/wiki/Synovial_fluid

http://www.eorthopod.com/public/patient_education/6597/septic_arthritis.html

http://www.labtestsonline.org/understanding/analytes/synovial/test.html

'Rotten Eggs' Gas and Inflammation in Arthritic Joints http://www.sciencedaily.com/releases/2010/08/100820101358.htm