The Shopping Scientist and Mr Rat Part I

The Shopping Scientist: So, what do you reckon Mr Rat?
Mr Rat: About what?
The Shopping Scientist: What you're eating.
Mr Rat: I'm not eating anything.
The Shopping Scientist: Yes you are. (sotto voce) The reporters are here, remember. Is it sugar Mr Rat?
Mr Rat: No.
The Shopping Scientist: Well, if it were sugar, and you were eating it, you might be able to tell us whether it was fresh and hence a good buy, mightn't you Mr Rat?
Mr Rat: Probably not.
The Shopping Scientist: Well, probably yes that should be, actually, shouldn't it? Because sugar is just one of the thousands of ordinary shopping items we test for value and freshness.
Mr Rat: Sugar doesn't go off.
The Shopping Scientist: Oh, I think you'll find it does. As you and all of the journalists gathered here would know, each packet of sugar has an expiry date.
Mr Rat: Which doesn't mean anything. And anyway, if you're relying on the expiry date to work out whether something's fresh, why am I here?
The Shopping Scientist: You know, I'm going to end this conversation now. I mean, no one forced you to test the Ratsack yesterday ... that is all I will say.