[SamwiseGamgee]

Wargs have indeed been known to dabble in the black arts, and it is quite possible that this warg you have is doing such a thing and leaving these 'presents'- possibly eye of toad and foot of newt- for you in some kind of Morgul taunt.
It sounds to me as though your warg is a dwarf dutch warg. They're famous for turning to other methods for proving themselves rather than the supreme power and physical prowess of larger breeds of warg.
However, there is one thing you must remember: you are not trully the master of this warg. the warg obeys no mere mortal, it merely submits itself as it chooses. 'Be wise in your treatment of the warg, for he forgets not lightly,' as Elrond once said.
Eomer, where are you, man? We need the original godfather of warg back for some great warg related stories!