Method calls on variables declared with type 'dynamic' are resolved at runtime rather than compile-time - the actual type of the instance is determined, and an attempt is made to call a method on that type with the appropriate signature. If such a method does not exist, a RuntimeBinderException is thrown.

This rule identifies calls to instances with the dynamic type where it can be statically determined that the call will throw a RuntimeBinderException.

Ensure it is not possible to make a call to a dynamic instance of a type that lacks the appropriate method signature for handling that call.

In this example the program attempts to call Foo on a class that doesn't have a Foo method. This program is guaranteed to fail at runtime with a RuntimeBinderException.

MSDN: dynamic (C# Reference).