If your passage floor looked like that you would be pretty upset knowing what caused it and why:

The cause of timber floor fluting (cupping) is a water leak getting under timber, swelling it and causing it to expand but why and where?

Thermal image provided answer where to look, inside this wall:

Although invisible to naked eye, thermal imaging provided leak location in seconds (dark areas on bottom of passage wall are colder than the rest of the wall because they are damp from water leak).

Before you start blundering about smashing plaster to look for leaks thermal scan could save you time and unnecessary damage.