The Not-Scientific Method

The language of the First Ones is not static like most others. It evolves. Creatures like the sentries are more advanced than your average poultrid, obviously. Their more complex thought processes give them an innate resistance to the invaders' overriding magic. But you should not take my word for it. We can actually test this! In the grotto there is a librarian. Take those phrases you memorized and infuse them into it. Then try out your helm.