Eternal sin
Thomas Aquinas lists, or has responded to, six sins that supposedly go against the Holy Spirit:
Thomas Aquinas explains that the unforgivability of blasphemy against the Holy Spirit means that it removes the entrance to these means of salvation; however, it cannot hinder God in taking away this obstacle by way of a miracle.
Zoophilia
In Part II of his Summa Theologica, medieval philosopher Thomas Aquinas ranked various "unnatural vices" (sex acts resulting in "venereal pleasure" rather than procreation) by degrees of sinfulness, concluding that "the most grievous is the sin of bestiality." Some Christian theologians extend Matthew's view that even having thoughts of adultery is sinful to imply that thoughts of committing bestial acts are likewise sinful.