I really like the contrast here. In both scenes we see Edward making a promise to Winry while pointing at her.
In the first scene he promises to make her cry tears of joy next time he does so (make her cry)
In the later scene he promises to give her half of his life if she did the same for him
Now usually when pointing your index finger at someone, you indicate that they are to blame of doing something wrong, when in this cases Edward is the one who is at fault.
It’s also interesting how in the first scene he points at her with his left arm - his real arm - but in the later he points with his right hand. When he lost his right arm he was practically forced into becoming left-handed so naturally, the first opportunity he gets, he starts using his right arm again.
Idk where I’m going with this anymore, I’ve just always found it interesting I guess