Proto-Slavic diphthongs developed into combinations of R and L with vowels, thus establishing new open syllables. This process is known as pleophony. It had its full effect in Ukrainian, Russian and Belarusian. At the same time, Bulgarian, Serbian, Czech, Slovak and Polish had a different effect of pleophony. This video describes initial pleophonic changes. It also shows a couple of ancient Germanic borrowings and their Slavic reflexes.
