VERY COOL. Dean and Geralt are going to take the contents of the sachet to someone who actually knows stuff. They'll be reaching out to Yennefer in a quick exchange.

The big questions are

1 - is that bug secretly a dude, don't @ him he saw that chick get turned into a lamb he has to ask
2 - is the sachet some kind of spell component pouch, if so what the hell spell uses a centipede and a seed
3 - if none of the above, can Yennefer deduce anything magical-adjacent from the contents, or just anything noteworthy in general?