Saw (Seated Rotation).
This is a building block exercise focused on helping you find functional spinal rotation and improve movement patterns. Improving spinal rotation is super important not only for the times you want to look behind you, but also because dysfunction in spinal rotation can contribute to some less than ideal movement patterns in the shoulders and hips, which in turn can contribute to all kinds of aches and pains.
The introduction is a bit longer because I wanted to share with you some anatomy and point out the finer details of this movement. The benefit of this exercise is the mindfulness, so the details are important!