'you're supposed to fire UP.. we BOTH fired UP!'

That singing bush scene was just hilarious.

Some comical looking bush starts singing american/english songs (err wouldn't it have been more realistic to hear spanish songs?) and then the amigos ask them "are you the singing bush?" (err what does it look like).

then they begin to use some funny sounding gibberish incantation to summon the invisible swordsman, both of them firing up in the air as they should.
Then chevy chase fires his gun sideways towards a mountain and you hear the
death cry "arrghh" of a man .. then a few footsteps then.. *slump*

Chevy defends his actions and says something like:
"how am I supposed to know he was there? he was invisible"

to which steve martin responded: "You were supposed to fire UP, we both (did) fire up"
That whole scene was just hilarious.