show.html.erb

<% if i == truncate_at_count - 1 %>
  <tr class="table-header">
    <td colspan="3" class="js-toggle-target text-center">
      <strong><a href="#expand-table" class="js-toggle">…and
        <%= attachments.count - (truncate_at_count - 1) %> more</a>
      </strong>
    </td>
  </tr>
<% end %>