GMA

You have to create an opportunity for them to find that
moment of mutual recognition and fun with each other ...
beyond the traffic, beyond simply getting images on the film.
You have to create some feeling about what's going on
chemically between the characters.

I have a pretty good sense about what an actor
would need in the given scene.
And if they are having trouble doing it I probably can understand why.

A director has to know everything: Psychiatrist, choreographer, ..., costume designer, .. when he shot Star Trek IV, which is unquestionable the best of the series, Nimoy had to become an ecologist and anthropologist, ... and even a rocket scientist. And when he shot Three Men And A Baby, Mr. Spock became Dr. Spock. But with all the preparation sometimes best is plain luck:

Tom Selleck was to lift up the baby and on queue
and suddenly there would be this fluid, dripping,
running down the babies leg and dripping of in
view of the camera. And we had now - I'm giving away
a secret here, but there is a point to it - we had
Tom's arm wigged with a a tube that
you couldn't see. And the tube ran

down the inside of his arm and ended at
his hand. And he held the baby in such a
way that on queue they prompt the fluid,
Properly colored...
On queue, it was not necessary for the
special effects-man to run the fluid through.
The baby... did exactly what was called for.