Volition formations (sankhara [sankhaara])* are like peeling a "banana tree"...

"Now suppose that a man desiring heartwood, in quest of heartwood, seeking heartwood, were to go into a forest carrying a sharp axe.

There he would see a large banana tree: straight, young, of enormous height. He would cut it at the root and, having cut it at the root, would chop off the top. Having chopped off the top, he would peel away the outer skin. Peeling away the outer skin, he wouldn't even find sapwood, to say nothing of heartwood (this is also like a peeling an onion..no eye in the center).

Then a man with good eyesight would see it, observe it, & appropriately examine it. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in a banana tree?

In the same way, a monk sees, observes, & appropriately examines any fabrications (volition formations/mental formation) that are past, future, or present; internal or external; blatant or subtle; common or sublime; far or near. To him — seeing them, observing them, & appropriately examining them — they would appear empty, void, without substance: for what substance would there be in fabrications?

Phena Sutta -Foam

*sankhara [sankhaara]:Formation, compound, fashioning, fabrication — the forces and factors that fashion things (physical or mental), the process of fashioning, and the fashioned things that result. Sankhara can refer to anything formed or fashioned by conditions, or, more specifically, (as one of the five khandhas) thought-formations within the mind.