The pun is built on the "prison" and "cell" words and this pun use a double-meaning presentation to execute its punchline. The "cell" word contains two meanings which are "the smallest structure of human body" and "the prison room". The person used these meanings at the latter of his first premise which is "the body felt like a prison". The person felt like he/she was confined because he/she made of "the prison room"
