A Bug's Life

Both: the herd migrates annually, and so do the cows. By an astonishing coincidence, they always do this at the same time, so when the herd is on its annual migration, the cows in the herd are on their annual migration.

A busful of tourists is making a three-point turn.
A busful of tourists are drinking themselves into a stupor.

In these two sentences, the tourists would not each be making their own individual three point turns, nor would the bus be knocking back the booze. But for the herd and the cows, no problem either way.