Function precheck

src/muse.c:58–160

Any preliminary checks which may result in the monster being unable to use * the item. Returns 0 if nothing happened, 2 if the monster can't do * anything (i.e. it teleported) and 1 if it's dead. */

 * anything (i.e. it teleported) and 1 if it's dead.
 */
staticfn int
precheck(struct monst *mon, struct obj *obj)
{
    boolean vis;

    if (!obj)
        return 0;
    vis = cansee(mon->mx, mon->my);

    if (obj->oclass == POTION_CLASS) {
        coord cc;
        static const char *const empty = "The potion turns out to be empty.";
        struct monst *mtmp;

        if (objdescr_is(obj, "milky")) {
            if (!(svm.mvitals[PM_GHOST].mvflags & G_GONE)
                && !rn2(POTION_OCCUPANT_CHANCE(svm.mvitals[PM_GHOST].born))) {
                if (!enexto(&cc, mon->mx, mon->my, &mons[PM_GHOST]))
                    return 0;
                mquaffmsg(mon, obj);
                m_useup(mon, obj);
                mtmp = makemon(&mons[PM_GHOST], cc.x, cc.y, MM_NOMSG);
                if (!mtmp) {
                    if (vis)
                        pline1(empty);
                } else {
                    if (vis) {
                        pline(
                            "As %s opens the bottle, an enormous %s emerges!",
                              mon_nam(mon),
                              Hallucination ? rndmonnam(NULL)
                                            : (const char *) "ghost");
                        pline("%s is frightened to death,"
                              " and unable to move.",
                              Monnam(mon));
                    }
                    paralyze_monst(mon, 3);
                }
                return 2;
            }
        }
        if (objdescr_is(obj, "smoky")
            && !(svm.mvitals[PM_DJINNI].mvflags & G_GONE)
            && !rn2(POTION_OCCUPANT_CHANCE(svm.mvitals[PM_DJINNI].born))) {
            if (!enexto(&cc, mon->mx, mon->my, &mons[PM_DJINNI]))
                return 0;
            mquaffmsg(mon, obj);
            m_useup(mon, obj);
            mtmp = makemon(&mons[PM_DJINNI], cc.x, cc.y, MM_NOMSG);
            if (!mtmp) {
                if (vis)
                    pline1(empty);
            } else {
                if (vis)
                    pline_mon(mtmp, "In a cloud of smoke, %s emerges!", a_monnam(mtmp));
                pline("%s speaks.", vis ? Monnam(mtmp) : Something);
                /* I suspect few players will be upset that monsters */
                /* can't wish for wands of death here.... */