A: Have you decided who will be in the starting lineup?

    B: We have already chosen four and so the remaining six of the candidates are on the bubble.

    Note: This idiom means “on the threshold, finely balanced between success and failure.” This American expression seems to have originated in the car racing community, in particular, the aficionados of the Indianapolis 500 race. If a driver was about to qualify and then someone did a better time and pushed him down the rankings into the non-qualifiers, then dreams of qualification would be dashed and his “bubble” would be burst. Another suggestion is the bubbling of water on the verge of boiling. The water on top of the bubble has two directions to go, either going up and evaporating or going down and joining the rest of water in the pot.