I love how fast Ninja’s facial expressions change… every picture is 1/10th of a second apart.
It make the process of capturing the perfect face a bit challenging, but also shows parts of his character. The first picture would fall under „serious face“ while it then changes to happy.
Also, if you take these pictures out of context, You can tell a totally different story.
I think, Ninja was only focused on taking the right steps in the first picture, as he walked carefully and then realized he was on top of the slope and continued happily onward.