If a unit is affected by, any characters with the unit and any model within the Stupid unit that do not suffer from being Stupid themselves must move as the unit moves. Remember, a character cannot leave a unit when it turns Stupid, because such a unit is bound by a compulsory movement rule. We can imagine he is trying to goad the Stupid creatures into activity, or perhaps he is pinned down or hemmed in by the dribbling brutes and unable to move of his own volition. Such models may not shoot in the turn the unit is Stupid.
If a character subject to Stupidity fails this test while he is within a unit, the entire unit is affected by Stupidity, as the troopers mill about in confusion because of the stupid orders they are receiving. Note that a Wizard subject to Stupidity cannot cast spells if he fails the test, but a Wizard that is not Stupid himself can cast spells even if the unit he is with is subject to Stupidity.