DNS prefetching is a feature of some browsers designed to reduce DNS resolution delays as users browse the web. This is done by extracting the domain names of links on a page and resolving each domain to an IP address without the user having clicked any of the links, so that if/when the user does click a link, the DNS query is already resolved. Prefetching may be applied to links that the user is likely to follow (such as the top search result in a search engine) or for URLs referenced by the page such as images, javascript, or CSS.
Catchpoint monitors do not perform DNS prefetching, as it can generate extra requests that would alter results, add unneeded DNS queries, use up additional bandwidth, and potentially create confusion when analyzing a site's performance.