@gemmi Let me have another go. For simplicity consider there are only 8 bottles and 3 testers let 1 represent bottle tasted by the mouse and 0 represent bottle not tasted by mouse Bot1 bot2 bot3 bot4 bot5 bot6 bot7 bot8 ms1 1 0 1 0 1 0 1 0 ms2 1 1 0 0 1 1 0 0 ms3 1 1 1 1 0 0 0 0 so if mouse 1 died bottle2 is poisonous which is obvious from chart. similar conclusions can be reached if mouse 2 and 3 died. Similar method could be extended for 1000 bottles of watertoo. Hope this is okay.