Exodus 22:1 speaks about the robber who was found "tunnelling in" to someone's house (vis-a-vis self-defense). Is that just a figure of speech, or did they actually go to that much trouble? (What were houses like back then?) I'd say try the door first ...
I since found that R' Hirsch and others say the word "machteret" simply means "breaking in", not necessarily tunnelling. But for those who say it means tunnelling (e.g. Radak) ... how would they explain?
Well you have to remember that in those days houses were not quite like they are today. The floors were earthen and they (the houses) were generally only 1 story high. So the simplest way to get into a house is to dig under the wall. Going through the front door is problematic: a) it's in a location where it's super-easy for the owner to notice (squeak) b) it might be locked c) neighbors may notice.
[if you really think it's so farfetched, I believe this exact method is used to steal the pearl in The Pearl]
Pure speculation here, since I don't have archaeological evidence to support this idea, but tunneling may also have been simpler (quieter, quicker, less noticeable) than breaking through a door. Picture a dog tunneling under a fence to get out of a backyard, not Andy Dufresne tunneling through concrete walls to escape Shawshank. Now try picturing a battering ram breaking down a heavy wooden door with a bar laid across it horizontally to keep it closed, not some secret agent slipping a credit card into the crack between the door and the door frame to release the latch. Which method do you think is easier?
As you know there is a Ganav and a Gazlan. A Ganav is someone who sneaks in and tries not to be seen. a Gazlan doesn't give a hoot. The Posuk is talking about a Ganav who tries to come in a way that he will not get caught.
As you suggest in your question, it's a figure of speech
(namely, why specifically did the Torah choose to use the example of a burglar "tunneling in")
In his commentary to Exodus 22:1 -- the verse about a robber found "tunneling in" -- Rashi writes:
אֵין זוֹ רְצִיחָה, הֲרֵי הוּא כְמֵת מֵעִקָּרוֹ
This is not regarded as a murder; it is as though he (the thief) has been dead from the beginning of his criminal act
This is to teach us that the burglar came with the intention of killing you, for the burglar knew that a person wouldn't sit idly by while their property is being stolen.
Rashi continues- thus the Torah teaches us the rule:
"אִם בָּא לְהָרְגְּךָ, הַשְׁכֵּם לְהָרְגוֹ"
“If one comes with the intention of killing you, be quick and kill him.”
The very next verse (Exodus 22:2) which is a continuation of the robber who "tunneled in" states:
אִם־זָרְחָ֥ה הַשֶּׁ֛מֶשׁ עָלָ֖יו דָּמִ֣ים ל֑וֹ שַׁלֵּ֣ם יְשַׁלֵּ֔ם אִם־אֵ֣ין ל֔וֹ וְנִמְכַּ֖ר בִּגְנֵבָתֽוֹ׃
If the sun has risen on him, there is bloodguilt in that case.—He must make restitution; if he lacks the means, he shall be sold for his theft.
To which Rashi explicitly writes:
אֵין זֶה אֶלָּא כְמִין מָשָׁל: אִם בָּרוּר לְךָ הַדָּבָר שֶׁיֵּשׁ לוֹ שָׁלוֹם עִמְּךָ
This is only a metaphorical expression: if the fact is clear to you that he is peaceably disposed towards you.
See also:
Sanhedrin 72a-b which discusses this topic extensively, as well as Rambam Hilchos Geneivah 9:7-13
