[Black Rose]

You can hook FM_Touch which will trigger on everything and print the classnames. That way you will find out pretty quick.

public plugin_init() {
    register_forward(FM_Touch, "Touch")
}
//...
public Touch(toucher, touched) {
    new classname[32];
    pev(touched, pev_classname, classname, charsmax(classname));
    server_print("Touched %s", classname);
}