It can be a little challenging to open the wallflower refill because the cap twists in the opposite direction (reverse thread) as you normally do to open a container.
Why do Wallflowers have a reverse thread? The reverse thread is used for safety reasons. When Wallflowers were first launched (almost 20 years ago), liquid plug-in products were very new. There were concerns that the device could be misused by twisting in products that were not design (and safety tested) with the Wallflower plugs, so the reverse thread was used to minimize the risk that the plug could be misused, and has been part of the Wallflower design ever since.