The trick to using the herbicide is knowing when to use it.

The trick of successful walking, I always say, is knowing when to stop.

The trick was knowing which situation called for what method.

"I got a few tricks up my sleeve, one of them is knowing you can be a big help in this."

A great trick to know - and to know when not to use.

The trick was knowing where to put them, but after three years on the job, he had all the major sources covered.

An old trick, but one these children did not know.

The trick is knowing which parts of the preparation are worth the effort.

The trick of finding someone who didn't wish to be found was knowing whom to ask.

But the trick is knowing exactly when those last six months are.