Hey @Gareth 

Welcome to the Klaviyo Community! 

Klaviyo tracks open events by placing a tiny, invisible pixel image at the bottom of every email. When an email is opened by the recipient, we record this invisible pixel (web beacon) as "viewed" and mark the email as opened. This method of open tracking is the industry standard. Because of this, it is possible (in rare cases) for a recipient to click an email without opening it, if they click a link before the email loads completely, if they have images turned off in their inbox, or if the email is clipped, amongst other reasons.

However, we also append each link with a tracking snippet, which is why you'll still see the clicks tracked, even if the pixel does not load. Hope this helps!