I didn't know this one until I saw ccp's answer and I don't know of a second way.
*foo = *`; $* = 1; "true\n0"=~/\z/;
*| = \$foo;
2 =~ /(2)/; *| = *^N;
xmath gave this one to me because it contradicted the documentation and it isn't supposed to be possible. There is a loophole but it requires reading an obscure bit from Changes5.8.
Snippets of code should be wrapped in
<code> tags not<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).