In this talk, I will present two investigations around dilute and dense granular matter, by going back and forth at the grain scale and at the material scale. 1) The dilute example deals with bouncing grains: when sand is sprinkled on a vibrated membrane, grains move until they eventually settle down in the nodes of vibration. These so-called "Chladni patterns" provide an easy visualization of the membrane's modes. However, there is no consensus on the mechanism by which bouncing grains migrate on the vibrated membrane. To explain quantitatively this phenomenon, we propose a statistical description of the grain motion. 2) The second part of the talk will focus on how cohesive forces between grains modify the flow of dense granular materials. Using experiments and numerical simulations, we propose two descriptions of this material: one continuous approach, where we extend the mu(I)-rheology, and one discrete approach where we investigate clustering and cohesion-induced roughness.