Mia and Me - Season 3 Episode 5 -

Mia and Sara are to milk the goats. These give only milk, if sung thereby. Mia and Sara sing merrily until the letter bearer appears with a letter. Mia finds out in Centopia that Yuko has a sister who lives in Blumental. The friends hope to find another heart crystal with Kuki's help. They suspect him in the cave of glowing mushrooms, but the entrance is blocked.