A couple of questions about meaning
Recently I've met several sentences in books which I do not understand correctly. Could you please explain the differences between these words?
1. From Heinlein's Door Into Summer:
"You must never pat a cat, you stroke it."
What's the difference between PAT and STROKE? It seems for me in Russian we have a single word for both these actions.
2. From Carl Sagan's Contact:
But you know the physician's staff, the symbol of medicine? Army doctors wear it on their lapels. It's called the caduceus. Shows two serpents intertwined. It's a perfect double helix.
Ellie: Well, I thought it's a spiral, not a helix."
I tried to google some images but it didn't help as the results of "helix" search is almost only DNA schemes =) And for me, DNA and caduceus look almost the same. Is there any extra meaning or is Ellie making smth up in order to win the argument? =)))