In this talk I will present several fluid mechanics problems that concern the flow of particles and suspensions. This topic has many variants, which I will introduce to provide breadth and perspective for the listener (most of you) who has not studied the topic. After the introduction I will highlight (i) shear-enhanced diffusion, as studied in a microfluidic device, (ii) axial dispersion due to shear-enhanced diffusion, and (iii) unusual structures formed when bacteria flow, and biofilms grow, in curved channels. Some answers will be given and pen questions will be indicated.