(See also this slightly different version)
Based on the original System 6/System 7 Macintosh system extension by Eric Shapiro and Ken Hornak.
Drag a file you don’t need into the trash and select “Empty…” from the Finder menu.
The command key keeps Oscar in the trash.
Warning! Children tend to throw lots of files into the trash in order to see & hear Oscar.
(And I’ve seen quite a few adults regress in such fashion as well!)
Spruced up a little with some better sound courtesy of a Sesame Street clip on YouTube.
Tested on Catalina (10.15) and above: Big Sur (11) and Monterey (12).
You will likely have to allow Oscar some permissions in your Security system preference pane ... Specifically, Full Disk Access. Not ideal, I know, but it’s the only way of monitoring your trash directory to see when it’s emptied.
If you are not in the mood for downloading and compiling source code, there is a zip file with a universal binary compiled for macOS here:
Downloadable prebuilt Macintosh version