“In the absence of reliable extensional rheology data, we can only point to the fact that when cats are deformed along their principal axis, they tend to relax more easily, suggesting that the extensional time is smaller than the shear time. Transient strain‑hardening can nonetheless occur. Second, because, flows of cats are usually free surface flows, the surface tension between the cat and its surrounding medium can be important and even dominant in the rheology, especially in CATBER (Capillary thinning and breakup extensional rheometer) experiments.” – M. A. Fardin, “On the Rheology of Cats”