The term for that is "going hollow". This is used in great effect in a specific point of the series (in rot13 to not spoil):
Gur svany svtug vf ntnvafg Tnry, gung'f orra frnepuvat sbe "gur oybbq bs gur qnex fbhy" fb gur tvey gung ur cebgrpgf pna cnvag n arj jbeyq. Ur jrag gb gur evatrq pvgl, sbhaq gur cltzvrf gung ner fhccbfrq gb pneel gung oybbq, naq sbhaq bhg gung gurve oybbq unq eha qel. Fb ur ngr gurz. Jura lbh ernpu unys bs uvf UC one, n phgfprar cynlf va juvpu ur oyrrqf ba uvf fjbeq, naq fnlf "Vf guvf gur oybbq? Gur oybbq bs gur qnex fbhyf?". Gur svtugf fgnegf ntnva, guvf gvzr jvgu Tnry svtugvat abg yvxr na raentrq ornfg ohg yvxr n zna ng uvf crnx. Ng guvf cbvag, ur nyfb orpbzrf ubyybj. Ur unf nppbzcyvfurq uvf tbny, naq gur ynfg guvat gb qb vf gb chg hc n tbbq svtug orsber qlvat sbe gur arj jbeyq naq gur tvey.
That was, to me, one of the most touching moment in the series.
Gur svany svtug vf ntnvafg Tnry, gung'f orra frnepuvat sbe "gur oybbq bs gur qnex fbhy" fb gur tvey gung ur cebgrpgf pna cnvag n arj jbeyq. Ur jrag gb gur evatrq pvgl, sbhaq gur cltzvrf gung ner fhccbfrq gb pneel gung oybbq, naq sbhaq bhg gung gurve oybbq unq eha qel. Fb ur ngr gurz. Jura lbh ernpu unys bs uvf UC one, n phgfprar cynlf va juvpu ur oyrrqf ba uvf fjbeq, naq fnlf "Vf guvf gur oybbq? Gur oybbq bs gur qnex fbhyf?". Gur svtugf fgnegf ntnva, guvf gvzr jvgu Tnry svtugvat abg yvxr na raentrq ornfg ohg yvxr n zna ng uvf crnx. Ng guvf cbvag, ur nyfb orpbzrf ubyybj. Ur unf nppbzcyvfurq uvf tbny, naq gur ynfg guvat gb qb vf gb chg hc n tbbq svtug orsber qlvat sbe gur arj jbeyq naq gur tvey.
That was, to me, one of the most touching moment in the series.