What is the ruling on placing a knife under a sick person's head, believing it will heal or fight devils, and saying "Ya Deen Muhammad" (O religion of Muhammad) upon waking up, and mocking the phrase "Ya Razi, do not forget me" written on tombstones?

It is impermissible to place a knife under a patient's head believing that it heals or fights devils, as there is no evidence for this, neither textually (in Islamic law) nor empirically. This act may constitute major shirk (polytheism) if the doer believes the knife is effective in itself, independent of Allah, or minor shirk if they believe it is merely a means and not effective in itself. The way to know causation is either through sacred texts (like honey and the Quran) or through observation and direct, clear experience. As for laughing at the phrase "the knife fights devils," this does not appear to involve mockery of religion or shirk.