Hm... that's the crucial question... Let's ask Ciel - He is the only person except for Undertaker who eat from that cookies~ ... Oh... I see, no comment from his side But I personally think they are normal cookies in bone style (maybe with vanilla taste~) & you?
They look too thin to be actual dog biscuits to me. It would be just like Undertaker to troll everyone into thinking he's a weirdo for eating dog treats when in reality they are delicious cookies. Makes sense, so that when he offers them to people they say no and more for him