It's because of R and L and to a lesser extent S. These are "syllabic consonants" (other languages have different ones, depends on pronunciation) which can take up the role vowels usually do because they can be stretched to an arbitrary length unlike other consonants.
Apparently English also has these, such as the M in rhythm or L in awful (the U is silent, so it falls on the L to form the syllable).
Honestly one of my life's greatest achievements in life was that I once used this to convince a Brazillian guy that Czech does actually make sense =D