Texture modified food and beverages allow managing swallowing disorders. The rheological properties of such drinks condition the risk of aspiration, post-swallow residues, but also the palatability and acceptance. The International Dysphagia Diet Standardisation Initiative (IDDSI) suggests the use of the syringe flow test for texture modified drinks. The syringe flow test consists of a fluid flowing out of a syringe under the effect of gravity for 10s and measuring the residual volume to determine the IDDSI texture level. The aim of this study is to better understand the syringe flow test and the relationship between rheological properties and the IDDSI texture classification. We established a simple theory considering the evolution with time of the viscous dissipation in the complex geometry of the syringe and the different fluid properties (rheological properties, density, and surface tension). A Couette shear cell was used to characterize the shear rheology of different shear thinning solutions of dysphagia thickeners. Several Newtonian fluids with a range of shear viscosities from 0.04 to 1.31 [Pa.s] were also considered. The theory was validated against the syringe flow measured experimentally. Besides quantifying the final residue in the syringe, the analysis of the IDDSI test dynamics was completed using video recording, image analysis and a computer linked balance. The simple theory shows a good agreement with the experiments, and the theory is in turn used to underline the rheological boundaries corresponding to each IDDSI textures levels. These results could be used to design drink flow properties to reach a desired IDDSI syringe flow test performance or identifying potential areas of improvement for such tests.