my $spawn = expect->spawn("ssh $_")

You have a typo in the above which the docs say should be

my $spawn = Expect->spawn("ssh $_")
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If you hadn't imported the expect sub then strict would have picked this up. ie:

$ cat et.pl
#!/usr/bin/env perl 
use strict;
use warnings;
use Expect ();

my $spawn = expect->spawn("foo $_");
$ perl et.pl 
Use of uninitialized value $_ in concatenation (.) or string at et.pl 
+line 6.
Can't locate object method "spawn" via package "expect" (perhaps you f
+orgot to load "expect"?) at et.pl line 6.
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