When Anthony says that he aims to choose a bride with his head and not his heart, I realized he’s actually pretty obviously talking to Benedict about BOTH Kate and Edwina. At first I thought it was just Edwina, but upon rewatching 50,000 times, I think it’s both - his head (Edwina) and his heart (Kate).
Benedict probably already knows that Anthony is attracted to Kate at this point. He knows she irks him for sure, but I think he also knows there’s something more there. Which is interesting, because this is the first scene we as viewers see after Anthony realizes Kate is Edwina’s sister.
Let’s look at the continuous dialogue without the Sharma scenes spliced in:
Benedict: Miss Sharma? (Benedict totally says this on purpose to imply Kate)
Anthony: Miss Edwina Sharma. Not the sister. Miss Edwina will suffice. It is only out of the greatest love for my family that I aim to choose a bride with my head and not my… heart. (not only implying that Edwina is his head, but that Kate, the alternative, is his heart. Benedict gives him a knowing smile. The more I watch, the more I think he’s smiling because it’s not just Anthony choosing with his you know what, but that it implies Anthony is choosing Kate specifically if he’s thinking with his you know what)
Benedict: Does Miss Edwina return your affection?
Anthony: *sigh* not yet. She would have done if it were not for the —
Benedict: The sisterrrr. (Again, Benedict pushing Anthony’s buttons) She’s rather thorny I take it.
Anthony: Indeed. She need not trouble me. Every rose does have its thorn after all.
I also think Anthony might have told Benedict about his convo with Kate on the terrace, perhaps also saying how he’s attracted to her. Or at least Benedict inferring it. Benedict asks Anthony in episode 1 if he is planning to offend every young girl until there are none left and if mother is aware. At first I thought he only meant the girls he’s been interviewing and at the ball, but the only girl he is shown explicitly offending is Kate. I know they don’t show Benedict being fully aware of Anthony’s love until later, but throughout the season, he enjoys Anthony’s agitation with Kate, and he gives knowing looks that could imply he knows he’s attracted to her, even from the start.
We also know that Benedict and Colin give knowing looks to each other during fencing. And again at Aubrey Hall. Love thinking about the siblings shipping them together. Just some more of my ramblings.