Killing Two Birds with One Stone
The first time Brianna heard this saying was sometime in the second grade. Her class read many fables and discussed the lessons that were conveyed through these fables. Since then Brianna has heard/seen it used casually throughout numerous books and movies.
However, she finds this phrase slightly odd and gruesome in its imagery. It invokes an image of the murdering of birds. If it is taken literally, the phrase tells a person to pick up the most aerodynamic useful stone in their vicinity, aim at a group of birds, and slay multiple innocent birds at the same time.
Like all English idioms, this idiom has an underlying meaning. In actuality this phrase tells a person that when he/she is faced with multiple problems it is best to find the simplest and most efficient solution; in particular a solution that will accomplish multiple tasks at once.
She would use this idiom in instances that if she had to drive at a long distance of 30 miles to complete a simple task, she might take the time to go shopping or complete another task while she is already there at a distance.
Since learning of its true meaning Brianna has adopted it as a familiar idiom that she uses often.