A study of Bach

Earlier today, I decided that I had grown tired of my heart.  So I had it replaced with a mouse.  

I went to the doctor.  He pressed his stethoscope against my chest and he looked concerned.  

"What's wrong, Doctor?" I asked.  
He answered, "Your heart is squeaking."  
"That is because it is not my heart, it is a mouse."  
"Ah," he replied.