Bitumen occurs as a solid or highly viscous liquid. Thus making the fluid much more viscous. A special pipette used in measuring viscous fluid such as whole blood. These pumps have application in fluid metering and pumping of viscous or shear-sensitive materials. These provide swarming motility on surfaces or in viscous fluids. Their unique design makes roller pumps especially suited to pumping abrasives and viscous fluids. Training in a viscous, buoyant fluid gave a better simulation. Tendons are viscoelastic structures, which means they exhibit both elastic and viscous behaviour. Stir bars also have difficulty in dealing with viscous liquids or thick suspensions. Lava domes are formed by the extrusion of viscous felsic magma. The problem with sulfur is that it makes molten cast iron viscous, which causes defects. However, not all stratovolcanoes erupt viscous and sticky lava. Dilbit (diluted bitumen) is a means of transporting highly viscous hydrocarbon. These react to form carbon dioxide, which is trapped in the highly viscous mixture. Lava flows of more viscous phonotephrite and trachyte erupted after the basanite.