When B.K.S. Iyengar was asked about his use of the timepiece (his watch, timing his āsanas) he explained that he was watching to see what gave up first. During very long holds of postures, he was looking for his weaknesses.
In this variation and stage of Dwi Pāda Viparīta Dandāsana, my teacher, Manouso Manos, taught us to lift the toes and metatarsals from the floor. In practice I watch to see what is tolerable to do for only a short time and then I revisit that repeatedly so the impossible gradually becomes possible and the weak places will gradually strengthen. This also helps with mental weakness. The noticing is what’s important when some part wants to avoid the work. Seeing that moment in practice (when I quickly come out of a pose or give up on an action after only touching it) is a gift— noticing and asking why? Repeating the intolerable makes it possible to see why it’s intolerable. That’s where the learning happens. Going back to the places that are hard, blind or scary brings alignment, balance to the imbalances, strength to the weak places, courage and illumination.
“It is by facing up to adversity and suffering, and accepting it as a necessary means, that our anxieties are resolved and disappear. If we are loyal to the path we are on, our lives will get better, and the light of distant perfection will come to illuminate our journeys.” Yogacharya B.K.S. Iyengar, Light on Life, p. 54.