Juiciness in a game or an app can be defined as all the effects such as sounds, zooming, or shaking elements. Although they are not indispensable to the game, they make the experience of gaming more pleasant.
The first thing we add is sound effects in order to give feedback to the user when something, either good or bad, happens in the game. For example, we could notify that the bird is flapping, or has hit the pipes, using a sound.
Basically, there are two ways for an indie game developer, which means a developer without any video game publisher's financial support, to add sounds to the game: creating them or searching for them from sound collections, such as https://www.freesound.org or http://www.freesfx.co.uk.
Because the aim of this book is to teach you how to create apps using Swift, we'll use some resources found in a free collection.
In the master branch, you can find .zip files with all the required sounds.
Note
You can find the sounds at https://github...