Under a microscope, a cell’s cytoplasm can resemble a tiny underwater version of New York’s Times Square: Thousands of proteins swarm through a cytoplasm’s watery environment, coming together and breaking apart like a cytoskeletal flash mob.Organelles such as mitochondria and lysosomes must traverse this crowded, ever-changing cytoplasmic space to deliver materials to various parts of a cell.Now engineers at MIT have found that these organelles and other intracellular components may experience the surrounding cytoplasm as very different environments as they travel. For instance, a cell’s nucleus may “feel” the cytoplasm as a fluid, honey-like material, while mitochondria may experience it more like toothpaste.