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Pretty much what Tom said, and you could give the reader enough to pick up on a hint that the plants are affected by infra red radiation by introducing a temporary source. Someone could light a fi...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/30410 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
Pretty much what Tom said, and you could give the reader enough to pick up on a hint that the plants are affected by infra red radiation by introducing a temporary source. Someone could light a fire in the cave, and a plant that was looking limp could look more healthy. Someone could stroke the leaf (or other part) of the plant, and the part they touched could change colour. The plants could appear to lean towards people as they pass, or petals could open when a source of heat comes near. That way, the characters don't need to know what's going on in scientific terms, but a reader will probably be able to come up with some theories.