crawl into one's shell
retreat into one's shell
go into one's shell

I retreated into my shell, being painfully shy in the first place.

But when asked to explain his success, Rocket retreated into his shy shell as if he were a turtle.

It tried to retreat into its shell.

If you retreat into your shell again when you reach Bajor, then you will learn nothing.

When conditions are dry, snails retreat into their shell and seal the entrance.

Despite retreating into its shell, China's government continued to state that it welcomed foreign business and investment.

He was his usual self once more, retreated into his bland and distant shell.

With that, his head pulled back from the doorway, like a turtle retreating into its shell.

We believe in linking national interests and we do not accept that it is right for each nation to retreat into its shell.

Controversy seems to always send Gore retreating into his shell.