As you've posted it, you have a syntax error:

syntax error at calling.pl line 1, near "'called.pl':"
Execution of calling.pl aborted due to compilation errors.
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And perldoc -f do explains the rest. :)

       do EXPR Uses the value of EXPR as a filename and executes the c
+ontents
               of the file as a Perl script.

                   do 'stat.pl';

               is just like

                   eval `cat stat.pl`;
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More at perldoc -f eval.