A Question about the poseball script

vector offset=<-0.0, 0.0, 0.1>;
vector Rotation=<0,0,0>;
string Hover="Sit Here";
string sit_button="Sit";

string animation;

set_text()
{
if (llStringLength(Hover)>0)
{
llSetText(Hover, <1.0,1.0,1.0>, 1);
}
else
llSetText("",<0,0,0>,0.0);
}

piemenu()
{
if (llStringLength(sit_button)>0)
{ llSetSitText(sit_button);
}
else
llSetSitText("Sit";
}

default
{
state_entry()
{
piemenu();
set_text();

llSitTarget(offset, llEuler2Rot(Rotation * DEG_TO_RAD));


}
changed(integer change)
{
if (change & CHANGED_LINK)
{

if (llAvatarOnSitTarget() != NULL_KEY)
{
llRequestPermissions(llAvatarOnSitTarget(), PERMISSION_TRIGGER_ANIMATION);
}
else
{
integer perm=llGetPermissions();
if ((perm & PERMISSION_TRIGGER_ANIMATION) && llStringLength(animation)>0)
llStopAnimation(animation);
set_text();
animation="";
}
}
}
run_time_permissions(integer perm)
{
if (perm & PERMISSION_TRIGGER_ANIMATION)
{
llStopAnimation("sit";
animation=llGetInventoryName(INVENTORY_ANIMATION,0);
llStartAnimation(animation);
llSetText("",<0,0,0>,0.0);
}
}

}

Hi
I wanna add for example a good-bye message when the sitting avatar stands up/lefts the ball . Where should I add it, can anybody help me please ?