The term 'Sang Part of 'Old MacDonald'' is referring to the popular children's song, 'Old MacDonald Had a Farm'. The crossword solution for this term is 'MOOED', which is the sound that a cow makes. This sound is featured in the song, as it is sung 'Old MacDonald had a farm, E-I-E-I-O, and on his farm he had a cow, E-I-E-I-O, with a moo moo here and a moo moo there, here a moo, there a moo, everywhere a moo moo.'