They found him at bed check. He'd swallowed his own tongue.
5 seconds sound clip from the The Silence of the Lambs movie soundboard.
You can hear this line at 00:22:06 in the Blu-ray version of the movie.
Quote context
[...]
- Sir.
- The orderly heard Lecter whispering to him all afternoon and Miggs crying.
- They found him at bed check. He'd swallowed his own tongue.
- Yeah. I'm... I'm still here, sir. I just... I don't know how to feel about this.
- You don't have to feel any way about it.
- Lecter did it to amuse himself.
[...]