Learn Finnish: Löysin tämän sattumalta, kun satuin penkomaan laatikkoa. - I found this by chance when I happened to rummage through the box.

The verb sattua (meaning 'to happen to') pairs with the -maan/-mään form of the action you happen to do, just like in the lesson's example satuin näkemään. Here, the verb penkoa (to rummage) takes this same ending to become penkomaan.

Are sattumalta and satuin related words?

Yes! They both come from the same root. Sattua is a verb that means 'to happen' or 'to occur by chance'. From this verb comes the noun sattuma (coincidence). When you put that noun in the ablative case, you get sattumalta, which translates to 'by chance'.

Why is the first object tämän while the second object is laatikkoa?

This sentence beautifully contrasts complete and incomplete actions. Finding something (löytää) is a sudden, completed action, so its object takes the total object case (the genitive-looking tämän). Rummaging (penkoa), however, is an ongoing process, so its object requires the partitive case (laatikkoa).

What is the exact difference between penkoa and etsiä?

While etsiä simply means 'to search for' or 'to look for', penkoa specifically means 'to rummage', 'to dig through', or 'to root around'. It emphasizes the messy, physical action of moving things around in a container, which is why it pairs perfectly with laatikkoa (a box or drawer).