[The Saucepan Man]

You raise some interesting points,akhtene.

In my earlier post, I had assumed that the Watcher made a bee-line for Frodo intentionally, but having re-read the passage, I see that there is no suggestion that this was necessarily the case. Maybe it did just go for the nearest tasty morsel, which would support the view that it was not a Servant of Sauron, but simply a fell beast that (by whatever means) found it's way to the lake before the Gates of Moria.

But, reading on, the description of the Watcher closing the Gates does suggest that it did so deliberately, with the intention of trapping them in:

Many coiled arms seized the doors on either side, and with a horrible strength, swung them round. With a shattering echo, they slammed, and all light was lost.

This, I think, was what led me originally to assume that it did deliberately go for Frodo, since it suggests some sense of purpose. If it was looking for a meal, why would it shut them in? Perhaps it was a Servnat of Sauron, after all.