In
Carve the selected faces inward. Pockets first, and a clean tunnel if you keep going.
In digs into the model. The first press sinks the selected faces into a neat pocket with walls; every press after that takes the same pocket one step deeper. Windows, mouths, and doorways all start as an In pocket. On the Grow card the action sits in the coral Remove group, named Dig in:
Punching through
Near the far side, the hint warns you: “One more press opens it right through.” That press punches a clean tunnel out the other side, for donut holes and archways. Ünflat never leaves a paper-thin skin or an open gap; it’s a pocket or a tunnel, nothing in between.
Changing your mind
Out reverses In step by step: it raises the pocket floor, and at the surface the pocket seals itself flush again. Undo works too.
What In needs
In carves solids. A flat sheet is refused with a hint to Grow it Out first for thickness. Faces that point wildly different ways won’t carve as one pocket; tap fewer at once. The shape of the pocket floor is up to the Scoop / Flat switch.