For example, sheep/sheep becomes shoop/sheep.
You mean like moose singular and mooms plural?
@zenvelo For example, yes. Or Meese.
Like fish and fosh, perhaps?
Carp and Crap?
On the fishy theme:
Koi and shy? Haddock and headache?
Deer and Dare. The females are Doe and Done.
Trout S: Trout P: Treat
Salmon S: Salmon P: Salmany
Spacecraft S: Spacecraft P: Spacefleet