Small notes a site leaves in your browser so it remembers you next time. They cannot infect anything — the concern is the ones left by other companies to follow you.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a stranger's bookmark slipped into your book.
For example
You put shoes in a basket, close the page, come back tomorrow, and the shoes are still in the basket. The shop left a note in your browser.
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.