Clue: With head oddly empty, bear reflected in wood, spluttering 'Huzzah!' (5-2-3)
Answer: WHOOP-DE-DOO
Explanation: Definition: Huzzah!
An envelope ('in') of HOOPDE, a reversal ('reflected') of ED ('h**E**a**D** oddly empty'- i.e. with the odd letters left out) plus POOH ('bear') in WDOO, an anagram ('spluttering') of 'wood'.