If I'm in the middle of taking a neder and I interrupt in the middle of a sentence to answer "Amen yehei shmei rabah..." can I just continue where I left off in expressing my neder or do I have to start again?
The Shulchan Aruch in Yoreh Deah 210:1 - סימן רי - שצריך לפרט הנדר בשפתיו - teaches us that when making a Neder you have to:
- Verbalize it
- Mean what you say and say what you mean
א: אֵין הַנֶּדֶר חָל עַד שֶׁיּוֹצִיא בִּשְׂפָתָיו וְיִהְיוּ פִּיו וְלִבּוֹ שָׁוִים.
לְפִיכָךְ הָיָה בְּלִבּוֹ מִפַּת חִטִּים, וְהוֹצִיא בִּשְׂפָתָיו פַּת שְׂעוֹרִים, מֻתָּר בִּשְׁנֵיהֶם.
אֲבָל אִם הָיָה בְּלִבּוֹ פַּת חִטִּים אוֹ פַּת שְׂעוֹרִים, וְהוֹצִיא בִּשְׂפָתָיו פַּת סְתָם, אָסוּר בְּשֶׁל חִטִּים לְבַד אוֹ (בְּשֶׁל) שְׂעוֹרִים לְבַד (דְּכֵן מַשְׁמָע בסי' רי''ז ס''ט) .
Which translates to (non-verbatim):
1: A Neder isn't valid unless you verbalize it and your words and intent match.
Therefore, if you mean to make Neder about [not eating] wheat-bread, but you mention "barley-bread", you are permitted [to eat] both.
But if you intended to [make a Neder not to eat] wheat-bread, or barley-bread, and you only mention "bread" then you are forbidden [to eat] whichever one you meant, but not the other.
So in your example, it would depend. If what you said (before or after the interruption) makes sense and is what you meant, then the Neder is valid, else it's not a Neder.
For example - based in the Shulchan Aruch quoted:
"I make a Neder not to eat" - interruption - "bread made of barley". Since you don't mean "not to eat", and "bread made of barley" doesn't mean anything, there's no Neder.
"I make a Neder not to eat bread" - interruption - "made of barley". Since you mean "bread made of barley" and "I make a Neder not to eat bread" can be sensibly interpreted as "I make a Neder not to eat bread made of barley", it's a valid neder.