What this video covers
The clip takes on the idea that no visible mold means no mold.
The three places it grows unseen are inside wall cavities, beneath flooring and within HVAC ductwork. All three are enclosed, frequently damp, and never inspected during normal life in a house.
The takeaway
Visible growth is a subset, not the whole picture. Smell, symptoms and humidity readings are what surface the hidden portion, which is usually the larger part.
Read the full written guide: Mold in HVAC Ducts.