There's a link to reply to every node that's visible, as far as I can tell. The Seekers of Perl Wisdom page has "[Offer your reply]" next to every node. If you click through to one of them, there's a blue bar between the text and the replies. In that blue bar is a link that says "Comment on" which takes you to a node to write a reply. Additionally, every reply has a "[reply]" link next to it that allows you to reply to that node.