[paulb73]

But surely it isn't wiggling the tissues by sound waves passing through matter, but by vibrating space time itself?

The skull shouldn't be able to resist gravity waves any more than soft tissues or 10km of lead?

[dotnet00]

When a gwave passes through, since the space contracts or expands, you get changes in density, since bone and soft tissue are different densities, there should still be a pressure differential that can be heard.

[rini17]

It does not directly change density of matter afaik, only exerts gravitational pull, same as Earth does, and that in turn influences the body. But unlike Earth's it rapidly changes in magnitude and direction.