The prototype version of Mario & Luigi: Superstar Saga contains a segment in the intro where Luigi actually talks in a speech bubble (as himself), which would not appear in the finished version or any other games in the series. In the final game, he only talks while disguised as Peach, and in Mario & Luigi: Dream Team, his thoughts are seen as text in the Dream's Deep area, but at no point does he talk without a disguise using text in a speech bubble as seen in the footage.
The two speech bubbles translate roughly to "Big brother! That explosion just now left us with a lot of voice bombs scattered around!" and "There are people in trouble. I wonder if anything can be done..." Luigi does not have any other written dialogue in the game, only communicating in the sound bites from the finished version.
He is referring to another element only found in the prototype, being the voice bombs placed around the area. In the finished game, those only appear in the cutscene of Peach's voice being replaced by bombs, and never in gameplay. Here, Mario can jump on them to disable them, and getting rid of one near a Toad will make him give Mario a Mushroom.
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