How does Perl detect this loop?

perl -we "sub fail {die 'test' }; END{ fail }; fail()"
test at -e line 1.
test at -e line 1.
END failed--call queue aborted.
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As you can see, die seems to get called twice, but then Perl determines that it is in an endless loop and stops. This is desirable behaviour, but I was a little surprised that it works... so I figured I would ask around to find out if this is a 'feature' and not just a fluke.