[Tutor] why does this not work

[Roelof Wobben]

Im trying to learn python by a course at codeacademy. Now I have this code : def shut_down(s):
    s = s.lower()
    if s == "yes":
        return "Shutting down..."
    elif s == "no" :
        return "Shutdown aborted!"
    else:
        return "Sorry, I didn't understand you"
    But when I run it  I see this message: It looks like output other than yes/no does not return 
"Sorry, I didn't understand you." So can anyone explain to me what I did wrong. Roelof  		 	   		  
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