grinding her pelvis into a fine mist

[JuriTerreni]

From TV series <Santa Clarita Diet>,

Dan found a finger in the Joel's backyard, and he knows it's Gary's. He's confronting with Joel, but Joel denies it.
Dan - And I know that Lisa saw Gary dancing with your wife at the club, grinding her pelvis into a fine mist. And then Gary disappeared.
What does "grinding her pelvis into a fine mist" mean? Thank you.

 

[johngiovanni]

When some materials are literally ground (down) in a grinding machine or using a grinding wheel, they are ground into a "powder" or a "dust". In a "fine mist", the particles would be even smaller.
Here "grinding...into a fine mist" is an image. It implies that Gary's dance movements were very, very sexually suggestive.

 

[Minnesota Guy]

Yes, exactly. Note that one definition of "grind" is: (in a dance) to rotate the hips in a suggestive manner.

 

[Barque]

You've probably understood this already but Dan's essentially accusing Joel of having killed Gary because Gary made an advance towards Joel's wife.