Glad that you've bounced back from health issues. 
I checked and have it working on one site, so have taken a quick look at the code that I used..
templates/your_template/content/contact_us.tpl.php
Right after the Recaptcha section around line 178 onwards
Code:
<!-- end modification for reCaptcha -->
<?php } ?>
</table>
</td>
</tr>
</table></td>
</tr>
<tr>
<td><?php echo tep_draw_separator('pixel_trans.gif', '100%', '10'); ?></td>
</tr>
<tr>
<td>
<table border="0" width="100%" cellspacing="1" cellpadding="2">
<tr>
<td class="main" width="150">
<?php echo ENTRY_ANTI_ROBOT; ?>
</td>
<td class="main">
<?php echo tep_draw_input_field('antirobot') . ' ' . (tep_not_null(ENTRY_ANTI_ROBOT_TEXT) ? '<span class="inputRequirement">' . ENTRY_ANTI_ROBOT_TEXT . '</span>': ''); ?>
</td>
</tr>
</table>
</td>
</tr>
Nothing else added in that file.
catalog/contact_us.php around line 28
Code:
// end modification for reCaptcha
$antirobot = tep_db_prepare_input($_POST['antirobot']);
Around line 97
Code:
// end modification for reCaptcha
// if ($antirobot != 'yes') {
if ( ($antirobot == 'yes') OR ($antirobot == 'Yes') ) {
$error = false;
} else {
$error = true;
$messageStack->add(contact_us', ENTRY_SECURITY_CHECK_ERROR);
}
Note the response to the question is also specified in the lines above
catalog/includes/languages/english/contact_us.php bottom of the file should look like this:
Code:
define('TEXT_REVEAL_EMAIL', 'Click to reveal email');
define('ENTRY_ANTI_ROBOT','Anti-robot question');
define('ENTRY_ANTI_ROBOT_TEXT','<- Type the word yes');
?>
Thanks @JRR - I missed the $messageStack->add('contact_us', change 
Note: this gives you scope to have different questions/answers for each of the forms, if necessary.
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