Howard Wolowitz:  Wha the hell is _ 43 _ ?
Raj Koothrappali: It 's a prime number . Encryption systems are based on prime numbers .
Howard Wolowitz: What kind of secrets would Sheldon need encrypting ?
Raj Koothrappali: Maybe it 's the secret to what makes his egg salad so delicious .
Howard Wolowitz: It 's paprika .
Raj Koothrappali: Really ? Well , one mystery solved .