Any tail that comes from a too-small arc or from improper power will do — those are the form’s two causes — and creep is just a way to make the arc too small without noticing. Miss and they may ask for a second. What is graded is the match: explain what you did, then keep casting.

What the instructor says

• Never stack two causes. Say shortened arc and only the arc changes; a power spike does not technically fulfil the obligation — the CI may tolerate it, the MCI will not.
• Three ways to make it dip. Arc: 100 to 110 degrees at 40 to 45 feet; cut 15 to 25 degrees off the stop. Spike: a wrist snap at the very end of the same stroke. Creep: the back cast stops short and the rod bounces forward — still the arc coming out too small, not a third cause.
• The stop does not move. The tip stops in the same place as on a clean cast; drift does not count, and 1/8 speed shows an early stop.
• Announce early. Call it midway through the previous cast.

Putting it to work

1. Build the tails in pieces: hand, noodle, rod without line, rod and line.
2. Pick one cause and change only that.

Source

From the FFI CI walkthrough series by Dayle Mazzarella (Chapter 3 — FFI Casting Instructor Certification Tasks, Fly Fishing Coach International), lesson 4, 00:00:46. See the video library and the task pages for the exam wording; terms follow the FFI Fly Casting Definitions.