Cornstarch suspensions exhibit remarkable behavior. Here, we present two unexpected observations for a sphere settling in such a suspension: In the bulk of the liquid the velocity of the sphere oscillates around a terminal value, without damping. Near the bottom the sphere comes to a full stop, but then accelerates again toward a second stop. This stop-go cycle is repeated several times before the object reaches the bottom. We show that common shear thickening or linear viscoelastic models cannot account for the observed phenomena, and propose a minimal jamming model to describe the behavior at the bottom. Concentrated particulate suspensions consist of a homogeneous fluid containing particles, larger than 1 μm. They can be found everywhere, and their flow is important in nature, industry, and even health care [1]. In spite of their significance, many aspects of the flow of these dense suspensions remain poorly understood. In order to study these materials, people have used methods inspired by classical rheology, and typically characterized them in terms of a constitutive relation of stress versus shear rate [2][3][4][5][6]. A general result is that, when increasing the shear rate, dense suspensions first tend to become less viscous (shear thinning) and subsequently shear thicken.Probably the most conspicuous example of a dense suspension is formed by a high concentration of cornstarch in water. Recent rheological experiments in cornstarch have revealed the existence of a mesoscopic length scale [6,7], a shear thinning regime that terminates in a sudden shear thickening [8], a dynamic jamming point [4], and fracturing [9]. Merkt et al. [10] observed in a vertically shaken, thin layer of cornstarch suspension that, among other exotic phenomena, stable oscillating holes can be formed at certain frequencies and amplitudes [10,11], which were subsequently described using a phenomenological model based on a hysteretic constitutive equation [12]. At present, however, we are still far from a detailed understanding of dense suspensions.In this Rapid Communication we subject a cornstarch suspension to a basic experiment, in which we observe and describe the settling of a spherical object in a deep bath of suspension. This yields two interesting observations. In the bulk, we find that the object velocity is oscillating in addition to going toward a terminal value. Near the bottom we observe a second phenomenon: The object comes to a full stop before the bottom, but then accelerates again, and this stop-go cycle can repeat up to seven times. We will show that both bulk and bottom behavior are conceptually different from that observed in a wide range of other fluids. We propose a jamming model for the stop-go cycles near the bottom that specifically includes the liquid-grain interactions.Experiment. Our experimental setup is shown in Fig. 1(a). It consists of a 12 × 12 × 30 cm 3 glass container containing a mixture of cornstarch and liquid. For the liquid we use either demineralized water or an aqueous solution of CsCl with...