Most surprising discovery/secret/unlock/experience in this game?

[Roger]

I guess for me is the codec calls you get depending on where you are or what you have equipped. Hearing a 5 minute talk about a cardboard box between Sigint and Naked Snake was stupidly entertaining for me the first time around. Knocking out Naked Snake with the cigar spray or handkerchief was also pretty hilarious. And also the Johnny Akiba grandfather bit was pretty damn hilarious haha. Anything secret I honestly can't recall that hasn't been said here.