There was a wave of murmurs that ran through the gathering crowd, considering what Thorax was offering them, but clearly apprehensive to accept it. Perhaps if they'd seen it for themselves, they'd be more willing to believe him, but at this time they just had reason to believe he was trying to trick everyone with his words. He could have changed into that form before arriving here, although from what you'd learned, creating something they had never seen was a difficult task for most Changelings.