Please watch!

Have you ever had a chick do this? I just got this baby chick. If it stands still long enough its body starts shaking. Almost like it’s wagging its butt back and forth. The first video is the worst that I’ve seen it happen but it’s usually like the second video, like just sudden shakes idk how else to describe it. It did have a little bit of pasty butt so I did wash the chick after taking this video. And I have added electrolytes and probiotics to its water. I’m not sure if it was just trying to use the bathroom? Or if something is neurologically wrong with it. Have you ever seen this before???