Involuntary movement ?

So my lo is 4 months, she does this motion which I have noticed a bit more now. But her right arm occasionally like goes up and down like

But a little faster. I’m not entirely sure what’s the cause. Her other arm doesn’t do it. She move her arm fine but it just randomly does that little motion and it’s starting to worry me. I’m keeping a close eye to see if theirs any triggers. I have a Drs app on March 1 so I’ll bring it up. Has anyone child experienced something similar ?