It has come to my attention (from a local Rabbi) that one is required to say a brocho on each and every bit of food he/she eats, unless he/she was thinking about that particular food at the time of the brocho.
The example he gave was that if I ate (and said a "ha'aitz" brocho on) an orange, if I later decide that I want to have grapes (before saying an after blessing, of course), I would have to say another "ha'aitz" brocho.
Now, this may be understandable for me in the case of the very different foods of grapes and oranges; they even require different after blessings!
Would this rule (of saying a separate brocho for each and every thing someone eats, without having it in mind at the time of the recitation of the first brocho) apply to foods which are much more similar? Like cheerios and pretzels, apples and oranges, etc.?
And if you will say that it applies to the above-mentioned example foods, would it also apply to, let's say, honey nut cheerios vs. multi grain cheerios? If so, would it even apply to the exact same type of food? (e.g. I have in mind one bowl of honey nut cheerios at the time if the brocho recitation, but once I finish I want to have another, would a second brocho be required?)
And lastly, what are the sources for this law of always having in mind whatever food which you want to be included in the brocho?