Rythmic swaying

Is Linguine just being a java fern frond? Does he really feel the beat? Is it a stress response? Is he okay??

I just got them on Thursday, so I am still getting to know them. They were also doing this in the first vessel I had them in, which was much smaller. I thought perhaps that they were displeased. I got them a larger vessel and some plants (and some more things on the way for them), which they have really seemed to enjoy. But when they're not napping in the leaves, they're doing the wave... Is this normal behavior?

Thanks so much!