it's been know for a long time, that when pets are taken into elderly (or sick) people, petting them promotes healing and health, both physical and mental. I've always thought a cats purr to be very soothing and relaxing.
Research has also shown very ill people who swim with dolphins have recovered health. Dolphins have shown interest in internal issues - like tumors - and do a lot of 'talking'. A dolphins talk has a huge range, from unheard high to unheard low. It also has a large range where the sounds are felt - vibrations you can feel in your body.
Now i'm seeing a report on healing with Didgeridoo's (Australian aborigine musical instruments) that have those low notes that are so deep, you can feel them.

so, i'm wondering if that isn't a research project in the making. sound vibration healing. non intrusive. soothing. and... healing? i should patent it and make a fortune. lol