This will help so that a person that has good interview skills can’t lead the conversation to where they want it to go and that interviewer gets comparable answer from all candidates. Another way to increase validity is to have a group of people interview a candidate and this may not be the best approach for an entry level job at a fast food chain, but this would help the bias of a single interviewer. This would allow all the interviewers to take notes and to compare what they saw or the lack there of.
The first behavior that I would expect to see from a good applicant would be a calm and cool demeanor. This would let me know that they are prepared and confident. Next I would expect to see some energy in the applicant because they are ready to get the job and get to work. Another thing would be someone socializing with the other applicants or even customers of Chick-Fil-A this again would show that they are excited and ready to be part of the team. Finally before interview starts I would expect a good handshake because this also indicates confidence and shows they respect me taking the time to interview