Smash vs be smashed

[TheBatman]

What's the difference between if you get hit by a bus your head will smash or if you get hit by a bus your head will be smashed

 

[Keith Bradford]

To smash is usually a transitive verb, so "your head will smash" is an unusual thing to say in any circumstances. But as a transitive verb it can be put into the passive, so "The bus will smash your head" can easily be turned into "your head will be smashed (by the bus)" .