SQUIRTLE's shell is not merely used for protection. The shell's rounded shape and the grooves on its surface help minimize resistance in water, enabling this POKéMON to swim at high speeds.
Fire Red:
When it retracts its long neck into its shell, it squirts out water with vigorous force.
Leaf Green:
After birth, its back swells and hardens into a shell. It powerfully sprays foam from its mouth.