Pseudomonas aeruginosa and Staphylococcus aureus are common pathogens of cystic fibrosis patients. P. aeruginosa uses retractable protein filaments called type IV pili to crawl along surfaces. The pili are too thin to see by light microscopy, but we can see their effects when they bind to objects and pull on them. In this video of a mixed P. aeruginosa and S. aureus culture, you can see a single S. aureus cell (centre left) being jerked in multiple directions by approaching P. aeruginosa cells. Other S. aureus cells are visible near the edge of the expanding P. aeruginosa colony biofilm. Although S. aureus is not motile, it can be transported by crowd-surfing with P. aeruginosa, contributing to the spread of co-infections.