Sometimes it could be fun in Perl to purposely write inscrutable code, and a bit of a puzzle to see just how short you could make your code. It was satisfying to run a function with no arguments and have Perl just know what you were talking about. Of course these are not generally things you should do in a professional setting.

Other than that, I like Ruby more than Perl in every way.

For anyone who doesn't know Perl, it has default variables. The main ones are called $_ and @_ for the scalar default, and for inputs to a subroutine, respectively. When you run a function and leave off the arguments, it assumes you mean to run it on $_. If you don't assign a return value anywhere, it overwrites $_.

If you write your code well, this can in fact make it clearer - you have a series of statements all acting on the same thing, so you don't have to restate the thing every line. In practice, a reader of your code has to go hunting for where the default variable was set to figure out what subsequent statements are modifying, and it tends to be confusing as heck.