It checks what arrives and what runs against known threats. A filter, not a force field — it lowers the odds, it does not remove them.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a guard dog trained on the smell of intruders.
For example
The guard dog catches the obvious intruder at the door. It does not catch the clever one who has a key and walks in politely.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.