$ perl -MO=Terse -e'scalar @_'
LISTOP (0x8133508) leave [1]
    OP (0x8133370) enter
    COP (0x8133400) nextstate
    UNOP (0x81333c0) scalar
        UNOP (0x8133630) rv2av [1]
            SVOP (0x8133540) gv  GV (0x8124334) *_
-e syntax OK
$ perl -MO=Terse -e'$#_+1'
LISTOP (0x8133440) leave [1]
    OP (0x8128040) enter
    COP (0x8133400) nextstate
    BINOP (0x8133508) add [2]
        UNOP (0x81333c0) av2arylen
            UNOP (0x8133630) rv2av [1]
                SVOP (0x8133540) gv  GV (0x8124334) *_
        SVOP (0x8133370) const  IV (0x8132bdc) 1
-e syntax OK