[BobK]

'Couple' behaves differently, depending on the point of view of the user.

The couple are leaving the registry.

They make a lovely couple.

These refer to the two people involved. (The second example makes it clear that a plural subject is the same thing as a singular complement.) But:

This ice-dancing is really dangerous. I keep thinking we're about to be knocked over by another couple - that couple, for example, is going far too fast.

Here the reference is to a singular risk. (In that context, you could use either singular or plural).

b