[wrqvrwvq]

For completeness, the transitive active might be "The terrorist blew up the bus". In the intransitive case you can infer the reflexive case (agent acting upon itself), "The bus blew itself up". Some languages have a formal "middle voice" for reflexion.

English lacks a formal middle and there is a good deal of established literature on verbal aspects where the subject is not really the agent called "ergative".

There is utility in comparing "the bus exploded", perhaps unclear as to the agent, but language is not an agent game. It's trying to convey information, which is clear enough in these cases.

[tptacek]

I like "the bus blew up the terrorist" as a clearer illustration. :P