Fank Klausz’s expanding strip in the bottom of the water-box reminds me of a technique I saw demonstrated in a museum in Japan many years ago.
Netsuke and other carvers wished to make protruding dimples on the backs of carved toads.
They carved the toad shape first; next, marked the positions of the dimples on the toad’s skin. The centres of each were punched with a device like a nail-punch that depressed the wood a couple of millimetres. The whole area was then shaved down to the level of the depressions and heated with damp cloths and hot irons. The depressions expanded back to their original shapes.
The result, after sanding and some detail carving, were some very convincing toads – warts and all.