A college student was in a philosophy class which had a discussion
about God's existence. The professor presented the following logic:

"Has anyone in this class heard God?" Nobody spoke.
"Has anyone in this class touched God?" Again, nobody spoke.
"Has anyone in this class seen God?" When nobody spoke for the third time, he simply stated, "Then there is no God."

One student thought for a second, and then asked for permission to
reply. Curious to hear this bold student's response, the professor
granted it, and the student stood up and asked the following questions of his classmates:

"Has anyone in this class heard our professor's brain?" Silence.
"Has anyone in this class touched our professor's brain?"
Absolute silence.
"Has anyone in this class seen our professor's brain?" When nobody in the class dared to speak, the student concluded, "Then, according to our professor's logic, it must be true that our professor has no brain!"

(...The student received an "A" in the class.)