[So the fact that she stole from pirates went completely over his head because there was something more important to clarify]

So it was not about stealing cats?

[Literal translation of the words there...

But as look at his hand, he showed her. The scale was a dark purple, almost blue color with an edge tinged in gold]

It is something that happens now as a merrow. Pretty much any amount of water will start the change, but only to the amount of water there.

[A drop of water encouraged a scale to appear because it was not enough to trigger a full change]