Write a function that tells you which TWO of its lines has been removed
Perl

sub foo {
    @a = (2..5);
    @a = grep $_ != 2, (@a ? @a : (1..5));
    @a = grep $_ != 3, (@a ? @a : (1..5));
    @a = grep $_ != 4, (@a ? @a : (1..5));
    @a = grep $_ != 5, (@a ? @a : (1..5));
}


This actually works for any number of lines removed (as long as it's not all the lines, that is), and can be trivially extended to more than 5 lines.  No helper functions are used, and it even uses only one statement per line.  It relies on the fact that, in the absence of an explicit return statement, the return value of a Perl function is the value of the last statement in it.

Note that (in list context) this code returns an empty list rather than the number 0 if no lines have been deleted.  This could be fixed (e.g. by appending "@a ? @a : 0;" to the last line), but would make the code uglier.  In any case, in scalar context it does return the number of deleted lines, which will be 0 if no lines have been removed. ;-)