During the first conversation with Clarice, Dr. Lecter mentions that he ate liver with fava beans and a good chianti. And this was not just a threat, but also a message to the viewer.

The novel that became the basis for the film reveals that dangerous and mentally unstable criminals must take a medicine that contains monoamine oxidase inhibitors. And these pills are completely incompatible with liver, beans, and wine.

There’s an assumption that Lecter hinted to Clarice and the viewers, in a very sly way, that he doesn’t take his medicine anymore and is going to escape, which is what he did in the end.