Commento su Tohorot 4:2

ספק נגע ספק לא נגע ספיקו טהור – and even in the private domain, and even regarding an individual who has awareness/knowledge to be interrogated who is holding the defilement/defiling object, because the defilement has no place that it rests upon, for all the while that it is in the mouth of the weasel or in the mouth of the dog it is not considered to be resting in any place, but rather it is passing defilement, therefore, its matter of doubt is deemed to be ritually pure, and even if the one who is holding the defilement/defiling object has awareness/knowledge to be interrogated.

A dead sheretz that was held in the mouth of a weasel that was passing over loaves of terumah and it is doubtful whether the sheret did or did not touch them, in such condition of doubt [the loaves] are clean. As in yesterday's mishnah, today's mishnah describes a case of moving doubtful impurity. The dead sheretz, a source of impurity, is moving for it is in the mouth of a weasel. Since the sheretz is moving and we don't know for sure if it touched the loaves, the loaves remain pure. However, you might just want to think twice before you eat them…