Google had brought some of their signature Doodles to the home screen search bar on Pixel smartphones last year. This year Google might be bringing that feature to some non-Pixel Android devices starting with a "Lab" experiment.
Google Labs made a comeback last week in the Google Search app for Android offering "a chance to preview work-in progress features like pinch-to-zoom on search results". The initial Labs features were fairly basic but over the weekend Google turned on the option for a third lab with the name - Search Widget Doodles.
For Google Pixel owners, this is a familiar feature as the Pixel Launcher's built-in search widget occasionally animates that day's Doodle into place over the usual Google G seen on the home screen. These mini Doodles have included all manner of things including baseballs to mark July 4, guitars for BB King, pretzels for Oktoberfest and snow globes for the holidays
However, the important thing here is that the new "Search Widget Doodles" Lab can be seen on any Android phone, not just Pixels. Given that Google can detect when you are using a Pixel device and the Pixel Launcher can enable and disable doodles, it looks like Google is indeed bringing Doodles to Android devices.
Since the Lab's recent arrival, no Google Doodles have been displayed on the Pixel or Android home screen widget so there isn't any information about how exactly this feature is going to work. However, from the "Learn More" link it can be seen that you need to restart your phone after turning on Search Widget Doodles.
So, it can be presumed that future Doodles will appear in the Google app's "Search" widget.
The Google app's "Labs" page is still in the process of rolling out to devices, and may not yet be available on your phone. To find the list of currently available Google Labs, open the Google app, tap More, then look for the Labs option.