For imagination's sake, say you have nothing available to you to train with but a single flat floor - no pullup bar/chairs/trees/etc., just a floor.
There are countless bodyweight exercises that can be done to build tremendous pushing strength in the upper-body, legs, and core. But what pulling movements are possible? For example, supermans and reverse leg lift headstands are great for the lower back. Can you think of any upper-body pulling movements?
Creativity welcomed!