I was at a friend's house the other day. She offered me Jello. She said vegans can eat Jello, "... there's nothing in there, right?" She was aghast when I told her what Jello was made from; to quote Merriam-Webster: glutinous material obtained from animal tissues by boiling.
Okay, so there's pulverized hooves in Jello. Vegans won't eat that. They can easily avoid that, but if you are a vegan for ethical reasons, how would you feel if the currency notes that you deal with had animal products embedded. Well, the new £5 notes came out in the UK and they have animal products.
According to a tweet from the Bank of England, "...there is a trace of tallow in the polymer pellets used in the base substrate of the polymer £5 notes." Tallow is the white nearly tasteless solid rendered fat of cattle and sheep used chiefly in soap, candles, and lubricants.
When I was much younger, I was a photographer. Imagine my horror when I realized that film was made from gelatin. Some things you can't fix (pardon the old photography pun there) and you just have to accept. You do what you can...