Despite being at the same time a very common and precious fluid, the rheological properties of blood have not been thoroughly investigated. In this manuscript, the rheology of swine blood is characterized. The rheology study is performed in shear flow and in uniaxial elongation. Measurements show that blood is a shear-thinning and viscoelastic fluid. The relaxation time and elongational viscosity of blood are measured. The relaxation time is found in agreement with a recent measurement by Brust et al. (2013). It is shown for the first time that the elongational viscosity can be 1000 times higher than the shear viscosity. Implications in biology and forensics are described.