What this video covers
The clip covers finding mold that is behind a surface rather than on it.
The signals are a musty smell that is stronger near one particular wall, and paint that is discoloured or bubbling. Bubbling means moisture is moving through the material from the other side.
The takeaway
Smell localises the problem better than sight does. If one wall smells different from the rest of the room, that is where to investigate, whatever the surface looks like.
Read the full written guide: Musty Smell in the House.