a fly
Examples
I want to write a novel so profound that it would suffocate a fly.
If a woman has to choose between catching a fly ball and saving infant's life, she will choose to save the infant's life without even considering if there is a man on base.
Doubts about the fundamentals of the gospel exist in certain churches, I am told, to a large extent. My dear friends, where there is a warm-hearted church, you do not hear of them. I never saw a fly light on a red-hot plate.
A fly doesn't enter in a closed mouth.
A blind man swallows many a fly.
Do not draw your sword to kill a fly.