The Animal Sniffer Plugin is used to build signatures of APIs and to check your classes against previously generated signatures. This plugin is called animal sniffer because the principal signatures that are used are those of the Java Runtime, and since Sun traditionally names the different versions of its Java Runtimes after different animals, the plugin that detects what Java Runtime your code requires was called "Animal Sniffer".
This mojo is designed to get a unique build number for each time you build your project. So while your version may remain constant at 1.0-SNAPSHOT for many iterations until release, you will have a build number that can uniquely identify each build during that time. The build number is obtained from scm, and in particular, at this time, from svn. You can then place that build number in metadata, which can be accessed from your app, if desired.