Is it really normal to get erections for weird reasons?

It's a scene from the movie.
It's an aisle at the store.
It's the view of a canyon.
The sound of a sword.

It's an orchard of peaches.
Your wife in the shower.
While you wait for appointments.
Or as you walk through the park.

Oh. uh oh. Erection.

(In case you want the music that goes with those lyrics: http://www.youtube.com/watch?v=9cLghY41klM )

The question: how often and what generally leads to an erection without any sexual arousal involved? Are these lyrics on point? Is it that normal to get a boner from the sound of a sword? Note that I'm not wondering about hard-ons from having sexual thoughts (I already understand those from a lady-boner perspective), I'm curious about the triggers for those random ones. Thanks for your time. Oh, and is erection-talk enough to give you one?