There have been volumes written on this, but assuming you aren’t up to reading volumes, here’s your shortcut, Leaned out scope creep identification cheat sheet.
1) Is the task/feature/assignment critical to the overall project deliverable? (And by critical, I mean can will the project be a failure without this?)
2) Was the task/feature/assignment included in the vision of the project? (Not necessarily the project definition document, by the way. Those miss things all the time. When you were under the table and dreaming, did visions of this thing dance in your head?)
3) Are the people best qualified to solve the problem or deliver said goods part of the project team?
4) Can the task/feature/assignment be discussed in project meetings without a team member gagging, wheezing or resigning?
If you answered “no” to any of these, it might be scope creep. If you answered “no” to all of them, it is certainly creepy. Throw some cold water at the person pushing the idea and get yourself (and your project) back on track.