Pullum, L 2011, 'What’s going on in there?', in R Jewell & AB Fourie (eds), Paste 2011: Proceedings of the 14th International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 389-403, https://doi.org/10.36487/ACG_rep/1104_34_Pullum (https://papers.acg.uwa.edu.au/p/1104_34_Pullum/) Abstract: Paste and thickened tailings both share similar properties, in that they appear to behave like homogeneous non-Newtonian fluids. Despite several publications on the issue, including various presentations at Paste conferences, the stratification of these materials, when subjected to a constant shear field, such as a laminar pipeline flow, still seems to be generally unknown. Design engineers design lines based on simple, small scale, rheological studies, using the assumption of homogeneous flow and the simplicity of a laminar flow regime. Such procedures generally under predict full scale operation, making large, or even full scale testing, appear to be essential. A review is given in this paper on research conducted by various groups, on such flows, in recent years, and describes methods that allow small scale testing to accurately predict full scale behaviour.