Fig. 1. 15 cycles of extension for a specimen of B. canaliculatum (see Rapoport and Shadwick, 2002). The bimodal behavior is delineated by the broken line at approximately 3% strain. Region `A' is the Hookean region and possesses an elastic modulus of 87.9 MPa, an order of magnitude greater than the 3.9 MPa modulus of region `B' (the yield region). The transition between the Hookean and the yield regions presents as apparent failure in the material, but is fully recoverable and repeatable. Arrows indicate the direction of strain during the extension cycles.