void main()
{
    // Gets the desired "Null Human" tag.
    object oAcid = GetObjectByTag("statue_acid");
    // Gets the PC.
    object oVictim = GetEnteringObject();
    // Name the desired spell from the list of spells in the "Constants" list.
    int nSpell = SPELL_MELFS_ACID_ARROW;
    // Assign the spell to the "Null Human" with whatever tag you had given it.
    // Be sure to give it a hide or whatever with "True Seeing" so they could
    // hit a stealthy rougue.
    AssignCommand(oAcid, ActionCastSpellAtObject(nSpell, oVictim, METAMAGIC_ANY, TRUE));
    // Thats all, instant projectile trap.  Only thing is there is no way of
    // disarming it.  It was not my intention to give that option, really.
}