Over the years I have had many passengers tell me about things they find strange. The first thing I do is thank them for their comment. Then I have a look and then explain what I have found. If I can't see what they told me about, I get them outside to show me. To date, nobody has found anything we didnt know about beforehand but plenty of items on the MEL have been spotted by eagle eyed pax. I hope they never stop looking.