Entity:FollowBone
Description
Makes an entity follow another entity's bone.
Internally this function calls Entity:SetParent( parent, boneid ), Entity:AddEffects( EF_FOLLOWBONE ) and sets an internal flag to always rebuild all bones.
If the entity vibrates or stops following the parent, you probably need to run Entity:SetPredictable( true ) clientside.
This function will not work if the target bone's parent bone is invalid or if the bone is not used by VERTEX LOD0