Flexing the Legs to the Chest to Float in a Pool

This page is the CodyCross answer for the clue below from Extraordinary Creatures, Group 1590, Puzzle 1 (Humpback Anglerfish).

Question is: Flexing the Legs to the Chest to Float in a Pool

and the answer is: TUCKING

Word Meaning:

TUCKING — present participle and gerund of tuck

Definitions from Wiktionary.