A coworker called me over on a problem he was completely stumped by. His boss was completely stumped by it, too. The problem looked like this:
my $foo = Foo->new;
Which resulted in the error Can't call method "new" on an undefined value.... I admit it had me stumped at first, but a quick session in the debugger and stepping through the code revealed the problem. Both 'strict' and 'warnings' were enabled, so the problem is not related to that.