The following is what the Ethereum documentation of Oraclize says:
Firstly, in the most common case, a transaction executing a function of a smart contract is broadcasted by an user. The function contains a special instruction which manifest to Oraclize, who is constantly monitoring the Ethereum blockchain for such instruction, a request for data.
Secondly, according to the parameters of such request, Oraclize will fetch or compute a result, build, sign and broadcast the transaction carrying the result. In the default configuration, such transaction will execute the __callback function which should be placed in the smart contract by its developer: for this reason, this transaction is referred in the documentation as the Oraclize callback transaction.
What kind of instruction is executed? What messages are passed around when calling the
Is the "special" instruction and
oraclize_query the same thing? As far as I understand,
oraclize_query is the request for data, right?
The other answers, don't address what the "special" instruction is, etc.