https://www.scienceworld.ca/stories/secret-power-cats-purr/
Why do cats purr? The science behind this feline phenomenon | Vet Radar.
" Pain relief
The vibrations produced by a cat’s purr have been shown to have pain-relieving effects. According to a study published in the Journal of the Acoustical Society of America, the frequency range of cats’ purrs is between 25 and 150 Hz, which is the same range that has been shown to have therapeutic effects on bone healing, pain relief, and wound healing."
