$ perl -MO=Concise,foo,-exec -e'{ my $x; sub foo { $x } }'
main::foo:
1  <;> nextstate(main 2 -e:1) v
2  <0> padsv[$x:FAKE:]               <-- Is "FAKE": closed over
3  <1> leavesub[1 ref] K/REFC,1
-e syntax OK