Yeah, the alerts on blank boxes can be a puzzle. I’ve been there several times and even in trial! It can be that the dog “catches” odor and just has that head snap look (and subsequent behavior since handler notices). Could be odor drifting over so a collecting odor problem. Could be contamination, tho’ that’s probably not as likely as people think. Usually there is some sort of confusion on the dog’s part. I’m still working on it with my dog but we’re getting there!
Now, for the distractors you WANT the dog to know the distractor is there but CHOOSE odor as more important. Easier said than done sometimes, but worth the time to work it.
Joyride K9 Dog Training