Shaykh Muhammad bin Saalih al-Uthaymeen rahimahullaah said:
Rats – a type of rodent – caused the flood of the dam by demolishing it.
They also destroy animal hides, especially water-skins that were used [in the times of old] to hold water; they destroy them and rip them open.
Likewise they steal gold – and this is something we have witnessed at home. We lost one of the women’s rings, so we searched and searched for it until we noticed a crack in the wall. And I knew prior to that that they steal gold. So we made the crack bigger and found the ring inside the hole.
And our Shaykh [Imaam as-Sa`dee] rahimahullaah informed us of a man who was writing in his room when a mouse descended from the roof and came close to him; so he placed a vessel over it and trapped it. After a while – when it had become delayed from its friends – one of them came looking for it to see where it had gone. It came to know that it’s friend was trapped underneath the vessel, so it ascended to the roof and returned with a gold coin. The coin was small, such that the mouse could easily carry it. It brought the coin and dropped it next to the man. Why?
[The students reply]: As a ransom.
[Ibn Uthaymeen rahimahullaah]: Or as blood money!
Anyway, the man said [to himself]: I will not release it. The mouse waited to no avail.
Then it ascended to the roof again and returned with another gold coin, and dropped it.
However the man said [to himself]: ‘Behind the hills is that which is behind them’. It continued to bring a third, fourth, fifth – until it reached ten – ten gold coins! It had become a collection!!
In the end it came with the bag. Indicating what? That’s it! All it had was finished. When the mouse brought the bag the man lifted the vessel and killed it[s friend]. He killed the mouse and the other one ran away.
In any case – this story I mentioned – my Shaykh [Imaam as-Sa`dee] rahimahullaah informed me of; indicating that from the harm and mischief of mice is their stealing of gold.
Similarly, they enter flour and contaminate it by defecation and other than that. So they are from the most corrupt of animals, and it is from the Sunnah (supererogatory) to kill them; even in the middle of the Masjidul-Haraam (i.e. the mosque of the Ka`bah).”
 The Shaykh rahimahullaah is referring to the story Allaah the Most High mentions in His saying:
لَقَدْ كَانَ لِسَبَإٍ فِي مَسْكَنِهِمْ آيَةٌ ۖ جَنَّتَانِ عَن يَمِينٍ وَشِمَالٍ ۖ كُلُوا مِن رِّزْقِ رَبِّكُمْ وَاشْكُرُوا لَهُ ۚ بَلْدَةٌ طَيِّبَةٌ وَرَبٌّ غَفُورٌ فَأَعْرَضُوا فَأَرْسَلْنَا عَلَيْهِمْ سَيْلَ الْعَرِمِ وَبَدَّلْنَاهُم بِجَنَّتَيْهِمْ جَنَّتَيْنِ ذَوَاتَيْ أُكُلٍ خَمْطٍ وَأَثْلٍ وَشَيْءٍ مِّن سِدْرٍ قَلِيلٍ
Soorah Saba; (34):15-16
[[Meaning: There was for the tribe of Sheba in their dwelling place a sign: two gardens on the right and on the left. They were told, “Eat from the provisions of your Lord and be grateful to Him. A good land have you, and a forgiving Lord.” But they turned away refusing, so We sent upon them the flood of the dam, and We replaced their two gardens with gardens of bitter fruit, tamarisks and something of sparse lote trees.]]
 An Arabic metaphor used to describe something suspicious, or a scheme/plot behind something.
It’s origin is that a slave-girl promised her male friend that she would meet him behind the hill when she finished serving her family at night. However they busied her and prevented her from going, until her longing for him overtook her, and she said: “You prevented me, and behind the hills is that which is behind them!”. [See: ‘Lisaanul-`Arab‘ of Ibn Manthoor]