I will start out with an introduction to classical micropipette aspiration assays in which biological cells deform when suction forces are applied. These experiments illustrate that pressure is an important parameter determining cellular mechanics. Traditionally, mechanical models of a closed cell contour, which resists stretching and bending and is forced outward by isotropic pressure, have been used to describe equilibrium shapes of cells. We use an extension to these models where the cell membrane is coupled to the actin cytoskeleton in order to explain where cellular blebs appear. Blebs are pressure-driven, fast cellular protrusions where the membrane detaches from the actin cytoskeleton. Our work shows that under certain conditions cellular geometry and physical forces can be the main determining factor for bleb site selection.