Hypophosis

"I have a hypophosis." He stated solemnly.
I tried not burst out laughing in surprise.
He proceeded with patient dignity, "Do you know what a hypophosis is?"
"What is it?"
"A hypophisis is an idea that you figure out."
"So what is your hypothesis?"
"My hypophosis is that this is the speaker of this car - where the sound is coming out!"
He put his ear to little odd shaped piece and pressed the button to hear the siren.
"I was right!" He declared emphatically.