From the imaginative point of view this rattle contains the powerful spirit that will raise the dead for the manipulation of the witches in their macabre ceremonies. In a way this rattle holds the spirit that they serve. The feelings the actors should focus on is the psychic weight of the rattle, the command that it gives them personally when they have possession of it and the desirousness to have possession of it.
The spirit of the rattle is very loosely based on the Voodoo Loa Damballa and the Christian Devil, though neither is truly being identified here - rather it is a particular mutation suited to the play landscape. Largely it is a strangeness (...weird sisters...) that implies both power and corruption of power by the witches...by Macbeth.