ÎÒÊÓÄÀ ÑÛÐ-ÁÎÐ ÇÀÃÎÐÅËÑß
[otkuda syr-bor zagor'els'a]
That's how the wet pine forest caught fire.
That's how it all started (usually about something unpleasant or troublesome).
Cf. That was the spark that set the forest on fire.