Can a Christian nun die smiling, and why is it not possible to infer the state of people of other religions from their faces at their funerals, and is it permissible to open a grave to infer the state of the deceased?

Such matters are not proof of a person's righteousness. Rather, they are considered only if the person adheres to obedience to Allah and His Messenger. For miracles (karamat) are for the pious allies of Allah who believed and were ever-conscious of Him.

Scholars have rejected the extraordinary feats and wonders that appear on those who transgress the Sacred Law. So, if you see a man flying in the air or walking on water, do not be deceived by him until you observe his adherence to divine commands and prohibitions.

Some wonders may appear on a misguided person, either as a test from Allah or a deception from Satan. Satanic states differ from miracles (karamat), for a miracle is only attained through the worship of Allah and avoidance of prohibitions.

Allah has made the torment of the grave a matter of the unseen for two reasons: 1. If people knew the state of the Barzakh (interim world), everyone would believe, and the believer would not be distinguished from the disbeliever. 2. If Allah had destined people to feel the torment of the Barzakh, they would not be able to bury their dead.

The basic principle is that those in this world cannot see the effects of the grave's torment on the deceased.