Disclaimer: Naruto doesn't belong to me.
He wasn't sure why he was surprised that she was strong. He had heard that she had been training under Tsunade, who, by all accounts, was incredibly strong. Despite what most people seemed to think, his arrogance came, not from over confidence in his abilities, but from his ability to accurately assess his opponents' abilities and to determine how to defeat them within minutes. He never underestimated his adversary. Only a fool did that. So he knew she was strong, not only physically, but emotionally. He had half expected her to start crying again when they met face to face. Now that they had, though, he was glad that she hadn't. Crying was annoying.
He had heard people compare her to flowers time and time again. She was a lily, a tulip, a cherry blossom, a rose. He had privately agreed with the last one when he heard it. She had always been so delicate, so fragile (so beautiful, but he never let himself think like that, even during his darkest moments, when he needed it the most), like a rose bud. So when she punched through solid rock right in front of him, one thought prevailed over all the others.
He ought to have remembered that roses have thorns.