What does the cryptic crossword clue "Animals vocalised on the way back (4)" mean?

The definition is "Animals". The wordplay uses a reversal. SUNG (reversal="‘vocalised’") = GNUS; definition: "Animals" The answer is GNUS.

Animals vocalised on the way back (4)

Guardian Cryptic #28975 | 26 Across | 2023-01-24 flower