An insect of the smallest kind,
If you transpose you soon will find,
That from all men I quickly fly.
Once gone, my loss in vain they'll mourn,
In vain will wish for my return.
Transpose me back, and you'll know why,
Now to kill me every art they try.

"Tsetse" can be transposed to "Testes".  Let's hope, for the sake of "all men", that's not the answer.