The timbre of an instrument is its unique volume articulation appearance sound

Timbre would mean the instrument's unique sound. The timbre refers to the unique or distinct musical note, sound, or tone that would help the listeners identify the different types of sound production. It would help the listener distinguish between a string instrument from a wind instrument, and so on.

The answer is cave paintings

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.