Perl's no keyword autoloads the module for you.

use Foo is an abbreviation for:

BEGIN { require Foo; }
Foo->import;
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The counterpart no Foo is an abbreviation for:

BEGIN { require Foo; }
Foo->unimport;
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Because import and unimport are just regular old subs, this means that modules can do their interesting stuff with no instead of use. It's a cute trick, though can confuse people.