Ward has a very specific way of talking about his physical injuries - namely, he doesn’t.
In 1x02, Skye notices the blood on his shirt and realizes that he’s been injured. As someone who has never seen combat, she’s shocked to see not just his injury, but how little it phases him. And it really doesn’t phase him. Ward barely responds, giving a sort of nonchalant shrug. He’s not just acting macho, he truly doesn’t believe it’s a big deal. As a specialist, physical injury is part of his job and he accepts it as a necessity.
In 1x18, she sees his bloodied face and turns his head towards her so she can get a better look at his injuries. By this point, Skye has seen plenty of combat and she’s been in the field, but his physical pain is no easier for her to stomach. It’s not something she’ll ever get used to, even if he is used to it. And just like before, we see how he shrugs off her concern, saying that it’s nothing. There is blood streaked down the side of his face and still, he says it doesn’t bother him. Again, we see how he considers pain to be part of his job description, and this specific injury - his beating at the hands of Garrett for the sake of maintaining his cover - truly is part of his job.
But in 2x01, we see a change in both of them. Skye sees the scar on his arm and does a little double take. She’s careful not to let the surprise show on her face, but the way she turns away at the end is very telling. She has always been keenly observant when it comes to him being injured, and this time is no different. But what is different is that this time, she actually looks away. This is the first time she has been unable to face his injury. It’s not just because she’s angry at him for his betrayal. Seeing his scar makes her genuinely uncomfortable because she knows it’s self-inflicted. She may believe that she hates him, but she still can’t turn off her empathy, and it’s difficult for her to see how low he’s fallen. And for the first time, instead of hiding his injury or discounting it, Ward tells her the truth. For the first time, he acknowledges his injury and recognizes it. And more than that, he explains to her very plainly what he’s been through and how he got his scars. It’s not an attempt at playing her or manipulating her - it’s a demonstration of his newfound resolve to be honest with her, no matter how it makes him look in her eyes. It doesn’t matter to him if the truth makes her pity him or see him as weak or hate him even more. When he promised to be honest, he meant it. And this is how he begins, by showing her the darkest, most vulnerable parts of himself.
Ward’s indifference to physical pain throughout the course of season one showed us the inhuman side of him. It showed us a man who was tough as nails, a man made of steel and kevlar. It showed us a man who lived up to Skye’s many nicknames - robot, T-100, Tin-Man.
But now, we see a different side of him. We see his weaknesses and his vulnerabilities. We see how he is tormented by his demons. Now, we see that he’s only human.