Servitors

Unless it includes a Techmarine, an unengaged unit that contains at least one model with this special rule must roll a D6 at the start of its turn.  
On a 4+ there is no effect this turn.  On a roll of 1,2 or 3, the unit is mindlocked until the start of its following turn.  
A mindlocked unit may not voluntarily move, shoot or charge. A mindlocked unit must still make compulsory moves, such as Pile In and Fall Back moves.