Bob Jewett said:
I'll go out on a limb here and say that if you have a gap between two balls and want to hit a third between them, it is impossible to hit the far ball first and move both of the "gap" balls.
Maybe, contrary to what I claim above, it is barely possible to move both of the gap balls, but if so, I suspect that only minor movement of the second gap ball struck is possible. ...
And after thinking about it some more, here is my explanation of why moving both gap balls is more or less impossible.
Suppose you hit the good ball after passing through the gap. Suppose you hit it on the right side. And suppose for the moment that the distances between the balls are small enough to ignore any draw.
If you hit the far object ball on the right the cue ball goes to the right and some amount forward. In any case, it makes less than a 90-degree turn. If it then hits the gap ball to the right, it could hit it on the left or right side. If it hits it on the left side (draw it out on paper) it will be directed generally forward along its original direction and not back towards the other gap ball. If the cue ball hits the gap ball on the right side, the cue ball will make another turn to the right. Again, this turn must be less than 90 degrees. With two turns to the right, each less than 90 degrees, the path of the cue ball cannot cross its incoming path. This means that it cannot hit the gap ball on the left.
However, if the far ball is well past the gap balls and you hit it nearly full with draw, it is possible to nearly draw the cue ball back through the gap and you will hit both gap balls on a good hit. I think this shot will look a lot different from Efren's shot.