Synonym for observee

I'm looking for a synonym for observee, i.e. something that is observed. The word observee doesn't seem be used much, so I would like to have a more common word if it exists.

I need to use it in a very abstract sense, so my example sentence doesn't get more concrete than this: "The observer watched the observee very closely."

Solution 1:

You may be able to reuse some terminology from software world here.

There is a standard software design pattern called Observer and its terminology may help. Quoting wikipedia:

The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

Also there is a Observable interface which may be implemented by observable objects. Quoting its description:

An observable object can have one or more observers.

[I know subject was a previous answer but I think this was too long as a comment.]

Solution 2:

I think the suggestion of subject that was given to you in a comment is probably best, but you could also go with specimen.