The sticky fluids found in pitcher plant leaf vessels can leave fractal-like fil- aments behind when dewetting from a substrate. To understand the origin of these filaments, we investigate the dynamics of a retreating thin-film of aqueous polyethylene oxide (PEO) solutions which partially wet polydimethyl siloxane (PDMS) substrates. Under certain conditions the retreating film gen- erates regularly-spaced liquid filaments. The early-stage thin-film dynamics of dewetting are investigated to identify a theoretical criterion for liquid fil- ament formation. Starting with a linear stability analysis of a Newtonian or simple non-Newtonian (power-law) thin-film, a critical film thickness is iden- tified which depends on the Hamaker constant for the fluid-substrate pair and the surface tension of the fluid. When the measured film thickness is smaller than this value, the film is unstable and forms filaments as a result of van der Waals forces dominating its behaviour. This critical film-height is compared with experimental measurements of film thickness obtained for receding films of Newtonian (glycerol-water mixtures) and non-Newtonian (PEO) solutions generated on substrates inclined at angles 0°, 30°, and 60° to the vertical. The observations of filament and its absence show good agreement with the theory. Further analysis of the former case, involving a stability analysis of the con- tact line, yields a prediction of the spacing (wavelength) λˆf between filaments as λˆηˆ/ϒˆ∝Ca, where ˆCa is the capillary number for contact line motion: our experiments yield λˆηˆ/ϒˆ∝Ca1.08 and earlier studies in the literature reported λˆηˆ/ϒˆ∝Ca0.945. The evolution of the thin-film shape is modelled numerically to show that the formation of filaments arises because the thin-film equation features a singular solution after a finite-time, hence termed a “finite-time sin- gularity”.