Itachi spared a dangerous moment to turned around, give his cousin and smile, and then avoid the branch that almost took his head off. This was actually a good way to test his endurance, and he was supposedly more "healthy" now, and if he did have a sudden collapse, he wouldn't really be endangering anyone.

He was annoying Obito, testing the team he was working with, and testing himself all at once. What could be better?