kazi islam , 18 , sent messages via blackberry to harry thomas , 19 , praising lee rigby 's killers and encouraging him to buy a knife to attack .
cake ' codeword for ` bomb ' , a court has heard .
islam , who is accused of preparing for acts of terrorism , used ` cake ' as code for bomb in his messages , but failing to understand his ingenious ruse , thomas replied : ` coming back to islam helped me that