NovMonk: You'll need to read about warnings (perldoc -f warn) but this may also help.

This generates a compile-time error if you access a variable that wasn't declared via use vars, localized via my or wasn't fully qualified.

In (perhaps oversimplified) words, Perl is exhibiting a bit of DWIMery here; "protecting you from yourself" or "helping you catch mistakes like typos in a $var name (eg $var somehow is typoed as $vqr

ps: take the advice at the top of that page, and use perldoc to obtain a fuller explation.