Direct transmission between teacher and disciple does not necessarely need elaborate words and detailed instructions.
Shechen Rabjam Rinpoche: Once, Patrul Rinpoche was with his close disciple, Nyoshul Lungtok. They were lying at night in the meadow above Dzogchen Monastery.
Patrul Rinpoche asked him "Lungtok, do you know the nature of mind?"
"Not really." replied Lungtok.
Patrul Rinpoche said: "Do you see the stars shining above in the sky?"
Lungtok said: "Yes."
Patrul Rinpoche "Can you hear the dogs barking down near Dzogchen Monastery?"
Then Patrul Rinpoche asked: " How is the nature of mind?"
At that moment Lungtok had understanding.
This is possible with pure connection and so great devotion.