What does the cryptic crossword clue "Thoreau's gag! Fell about in fits of giggles! (15)" mean?

The wordplay uses an anagram. anagram of THOREAU'S + GAG! + FELL = GALESOFLAUGHTER The answer is GALESOFLAUGHTER.

Thoreau's gag! Fell about in fits of giggles! (15)

Independent Cryptic #11673 | 5 Down | 2024-03-09 flower