Hey, Samorost is one of my favorite games! That was not intentional, but thanks a lot, it's a great compliment! :)
Yes, we are aware that our game is not very intuitive as it is... Among other, we didn't have time to provide feedback for the player...
The slimes will always try to go in the direction of their home planet, and left clicking anywhere on the screen will make them curious (only for a few seconds). That way, you can attract them manually.