it boils down to:
1. lie on your back on a flat surface
2. pull your feet towards your butt without raising your butt
3. stay like there for a few minutes
ideally if the surface youre on is grippy enough (sports mats?) then you won't need much effort to keep your legs like that and it actually lets you relax your lower back much better than just laying flat
luna the doggie 
@lunareclipse@snug.moe
