The Djra Codex
Silk is a creature called a Xolobo. Xolobo's are war mounts used by the Djra's army (the Fury. Headed by the Raze King). When noteable soldiers' xolobos die, their bones are dipped in tar and sent back to guard their masters' tombs. Bones (xolobos or soldiers) are typically escorted back to the soldiers' hometown. It's a great honor.