The right word
Which word will bring which effect? The answer, of course, depends on the context.
As I reviewd Parashas Noach, I recalled a lecture that Rabbi Copperman delivered about the effect of language and why particular expressions are employed in particular contexts in the Torah. When Noach is directed to gather the animals into the ark, he is told to take a pair of each (Bereishis 7:2):
וּמִן הַבְּהֵמָה אֲשֶׁר לֹא טְהֹרָה הִוא שְׁנַיִם אִישׁ וְאִשְׁתּוֹ
and of the animals that are not clean, two, a male and its mate.
That formulation is repeated agin in the eight verse:
מִן הַבְּהֵמָה הַטְּהוֹרָה וּמִן הַבְּהֵמָה אֲשֶׁר אֵינֶנָּה טְהֹרָה Of the clean animals and of the animals that are not clean
It's particularly striking because the Torah doesn't add in excess words, and it is possible to write this in shorter form if the single word tameh were substituted for the two words lo tehorah or the three asher ayenena tehorah. The Talmud in Pesachim (3a) refers to the second formulation in quoting R' Yehoshua ben Levi's declaration that a person should never utter an offensive word, as we learn from the roundabout way the Torah referred to the unclean animal in this context, adding on 8 additional letters to the text.
אמר ר' יהושע בן לוי לעולם אל יוציא אדם דבר מגונה מפיו שהרי עקם הכתוב שמונה אותיות ולא הוציא דבר מגונה מפיו שנאמר מן הבהמה הטהורה ומן הבהמה אשר איננה טהורה
This is a very nice lesson for being careful about speech, but you should have a question. In numerous other places, the Torah does use the term tameh to describe animals that are not kosher. So if it is not as nice to use that direct expression, why does it do so at all?
Here's the difference between the lightning and lightning bug in context. When the animals are described for the sake of saving them, the Torah uses the longer, nicer expression. But when it comes to warning us which animals are forbidden for us to consume, then we need the direct, "call a spade a spade" approach to clarify that they have to appreciate their tameh status in that context.
As I recall, Rabbi Copperman connected this to an expression we see several parshios later. In Parshas Miketz (42:1) Yaakov tells his sons:
הִנֵּה שָׁמַעְתִּי כִּי יֶשׁ שֶׁבֶר בְּמִצְרָיִם רְדוּ שָׁמָּה וְשִׁבְרוּ לָנוּ מִשָּׁם וְנִחְיֶה וְלֹא נָמוּת
"Behold, I have heard that there is grain being sold in Egypt. Go down there and buy some for us there, so that we will live and not die."
Rashi comments on the words רדו שמה:
ולא אמר לכו, רמז למאתים ועשר שנים שנשתעבדו למצרים, כמנין רד"ו:
He did not tell them, "go," but "go down," hinting to them with the gematria of those three letters that they would remain enslaved in Egypt for 210 years.
Your question should be: why would he say merely "go," when we know that any exit from the land of Israel is considered a descent, which makes the verb for going down the right one? That's why we have to remember the lesson from Parshas Noach. There is a negative connotation in the command רדו that normally would have prevented Yaakov from using it in addressing his sons. The fact that he did indicates that there is particular significance to the word in this context, and that is the numerical value.