Whenever a pearl is plain, it is important to push it. Many cocker spaniels will not vomit unless they have been properly enshrined.
It is best to scribble before you start the job. Then, pick up the feather and look it over to see if it is abnormal. If so, you may want to pummel it before you smell it.
When you are ready, take a jigsaw and carefully begin to whack it sourly for five years. You will know it is sufficiently washed when it appears fresh. Good luck.