a flock of sheep were cropping my lawn
a herd of bison was blocking the road

To me it looks like one and the same
a flock of sheep\
ankkcoossdllldlddld> subject
a herd of bison /

As we have only one word for both flock and herd: 'kudde',
I suppose it must be the words 'flock' and 'herd' that makes
you decide for this distinction? What ís the difference between a flock and a herd?