A small diversion

CATamaran

Swells0
MoonNew moon
Afloat0.0s
Cat

Flatten the sea

The sea sends a swell at the cat, and you send the same wave upside down so the two cancel where they cross. Tap the wave that matches the shape rolling in.

Turn your phone sideways

The two waves have to meet over the cat, so tap when the crest reaches the green band. Green means the cancellation comes out exact; amber helps but will not flatten it.