Other than it first being mentioned about 10years later?
Or the inherent implausibility of it as a method of murdering somebody? I mean, it'd work, obviously. But it's a lot fussier than the more likely stangulation/smothering and much more likely to lead to discovery either during or...
The whole "poker up the bum" thing was first mentioned about 10years after he died. It doesn't make sense in context as he was killed after a number of rebellions (that he had no real part in) aimed at restoring him to the throne, not because of anything directly relating to his relationship...