The idea for this app is great which is why I gave it 4 stars. Hopefully the developers will improve it because it is lacking a lot of key information at this point.The bulk of this app is an interface that allows you select muscles, muscle actions, and facial expressions from vertical columns and a drawing of a face which will change based on which muscle action or expression you choose. You can choose actions and create your own custom expressions.Selecting a muscle highlights in red actions and expressions that use it. And the same thing if you select an action or expression. Unfortunately, the highlights are not complete and many things are left out. For instance mentalis does not highlight sadness despite being the “crying muscle.”Even worse is that many muscle actions are not included, making it impossible to make many expressions, including basic expressions. There is no open surprised mouth. No triangular fear mouth. No crying mouth with mentalis bulge. No crescent joy eyes. No squinting eyes. There is no distinct brow for fear or sadness, just a generalized “brow of distress.” Most of the actions are extreme forms, so not many subtle expressions are possible.The translation from Spanish is also poor, but this is a minor issue since the app is mainly visual.Despite these complaints the app is good for what it does include although I think it is overpriced at this level of incompleteness.