Knock Knock Knock, Penny!
The Theoretical Physicist always knocks thrice.
The signature knock consists of three knocks before stating the person's name, it is then repeated two more times.
The minimal artwork captures the obsessive compulsive tendencies of one of TVs beloved characters and simply wearing it will raise your IQ by a few points (results may vary).
This awesome white design is printed on a Red 100% cotton Redwolf tee.
This is a parody/fan-art design and this is not official merchandise.