Thanks for the answer. That worked. Thought it would be something more "active" like position next to alien, click on convert button or so.

I saw that you use a bunch of open source libraries. Do you use a standard GUI library for your game or did you create you own GUI system? The GUI is excellent, very clean and the text is crisp and very readable (thanks FreeType ).

Sadly not all independent games such good GUIs.

Yeah, a manual would be nice. Just started my first game, researched "pheromators" (or how they may be called in english) and have no idea how to use it to convert aliens.