"The Fifth-Column Mouse" is a bad cartoon from Looney Tunes...something you'd just never expect. In fact, I had to check twice to see that it WAS from Looney Tunes, as qualitatively it's well below the quality of their other early 1940s output. The cartoon is not funny and it features a lot of singing...and it's incredibly dated. No wonder I found this on a Roku channel...as apparently Warner Brothers (who owned Looney Tunes) hasn't bothered keeping the rights to it!
The cartoon is a very obvious parable about appeasement...the type that Neville Chamberlain and his likes did with Germany before WWII began. A mouse is caught and instead of the cat eating him, he hires the mouse to be his spokesman and convince the other mice that the cat likes them! This lasts for about 30 seconds and then the cat is out to eat the mice. The mice respond by mobilizing for war...along with a lot of annoying singing.
Overall, a bit of a chore to watch this propaganda cartoon and it just isn't funny.