If there wasn't a .object file in there, then you need to put them in manually.
>>Put all the files that were in that folder into FeralHeart\Media\Objects\MyObjects.
>>Relaunch the game and go into 'Object Maker'
>>In the 'Object' Section, open up 'Rock' that is in 'Default'.
>>Select the Rock object and go to the 'Mesh' section.
>>Where it says rock.mesh, delete the word rock and replace it with the name of your new mesh.
(Example; rock.mesh turns into pillow.mesh)
>>That's it! It should turn into the mesh you're wanting.
>>Export/Save the Oblect into it's own Group (Example; HammyMeshes)
Good luck!
