One way to hold this phrase is to picture a patch of land where numbers go up. Animals do not scatter to have their young; they come back to one place, and by the end of the season there are far more of them than there were at the start. The useful part of that picture is not that something is present there. It is that the place itself is doing the multiplying — which is why English can point at a street, an office or a comment thread and use exactly the same words.
「breeding ground」可以想成一塊「數量會變多的地」。動物不是隨便找地方生小孩，而是特地回到同一塊地；一季過去，那裡的數量就比原本多了好幾倍。這個畫面真正有用的地方，不是「那裡有東西」，而是「那塊地本身讓東西一直長出來」。也正因為這樣，英文可以指著一條街、一間辦公室、一個留言區，用一模一樣的字。
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