The term comes from the Owl and the Pussycat, The Duck and the Kangaroo, by Edward Lear. Roo-matiz is slang for rheumatism. In the verse, the duck wishes to climb aboard the kangaroo so it can see the world. The kangaroo's objection is that the duck's webbed feet are cold and damp and it would give him the roo-matiz. Rheumatism was a term used to describe arthritis- like pain in the joints and soft-tissue. It is no longer medically used because over 200 different conditions can fit the description of rheumatism. Fibromyalgia and arthritis are more modern terms that are used. People have thought there is a link to joint pain, and weather, cold and dampness. Thus, the kangaroo was wary of carrying the duck on his back due to the damp and cold webbed feet.