Animate the error messages displayed each time they're triggered.
jQuery(document).ready( function($){
$(document).on('OptinMonsterOnError', function(event, data, object){
var l = 20;
for( var i = 0; i < 10; i++ )
$( ".optin-monster-error" ).animate( { 'margin-left': "+=" + ( l = -l ) + 'px' }, 50);
});
});