2,727. What Is Possible to Prohibit With a Vow

Hilchos Nedarim 1:6

If someone prohibited himself from eating figs and grapes, either in one vow or in two separate vows, both things combine to make the volume of an olive. The same is true in all comparable cases.

Hilchos Nedarim 1:7

If someone says, “This produce is an offering to me," or "like an offering to me,” or if he tells another person, “Anything that I eat with you is an offering/like an offering/to me an offering,” they are prohibited to him. This is because it’s possible that someone might make a vow for an offering, thereby sanctifying a secular animal, rendering it prohibited.