The gemara (Nazir 4) darshens from the pasuk “kol asher yeitzei m’gefen ha’yayin” that there is a halacha of tziruf with respect to issurei nezirus. Meaning: the Torah prohibits eating chartzanim or zagim (different parts of the grape). If a nazir ate half a zayis of chartzanim and half a zayis of zagim, even though each is individually less than a shiur of issur, the two are viewed as combined (tziruf), and since a k’zayis in total was eaten, the nezirus has been violated.
The Brisker Rav points out that there are two possible ways to understand this din. One approach is that “kol asher yeitzei m’gefen ha’yayin” teaches that the issur of chartzan is violated even if only ½ a k’zayis has been eaten provided there is a tziruf with other issurei nazir, and vice versa, the issur of zag is violated even if only ½ a k’zayis is eaten provided there is a tziruf with other issurei nazir. But there is another possibility. Perhaps the issur of zag and chartzan are only violated if a full k’zayis is eaten of each individually. However, “Kol asher yeitzei...” is a new independent issur that includes under its umbrella eating any of the different items such as chartzan, zag, etc. as long as in total a k'zayis is eaten.
The chakira of the Brisker Rav may underly the positions of Rambam and Ra'avad in the following dispute: The Rambam (Nazir 5:8) writes that a nazir who eats a k’zayis of grapes, chartzan, zag, raisins, and drinks a revi’is of wine is chayav 5 separate malkos (plus bal yachel). The Ra’vad asks why the Rambam left out a 6th set of malkos for “kol asher yeitzei m’gefen ha’yayin”. According to Ra’avad, “kol asher yeitzei..." is a new issur subject to malkos. According to the Rambam, "kol asher yeitzei…” simply teaches that tziruf applies to the individual issurim of grapes, raisins, chartzan, and zag, but is not an independent issur in its own right.
(Note: this is a bit difficult to fit into the sugya on daf 38, but those learning daf yomi can worry about that in a few weeks : )