Or when it doesn't contain a class name:

package Test;

sub foo {};

package main;

if (Test->can('foo')) {
    print "Hardcoded can works!\n";
}

my $t = 'Test';
if ($t->can('foo')) {
    print "Variable can works!\n";
}
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Now you or I wouldn't usually let that pass in a code review, which is why I go the extra step of invoking UNIVERSAL::can(). But we both know one dirty little secret of OO Perl, that it's the class name that's important, not the fact that something has been blessed.