Ooh, it had to hold itself back. Not yet, it could not do anything just yet. Not until they were out of sight. Its eye narrows ever so slightly, giving Stanley a Look™️.
And, with that, it swims much faster, using that tentacle to make sure Stanley didn't fall off.
Ahah! A cave, along a cliff face... File approaches it, but doesn't yet enter, peering inside.
"Would this work?" A soft bed of sand at the back, the front being a nice little bay of water. It would fit him well, he thinks...