The search engines are motivated to deliver value so they need to be able to ensure high quality appropriate content for each and every search request.
The rest are automatic, such as clicking a pre-configured link or having the browser execute request within a web page (for example, requests to call images and additional content from third party sites).
The law allows Web sites to host infringing content if they're not purposefully profiting from it and if they remove it at the copyright holder's request.