Unicorn for this puzzle: http://zeroturnaround.com/fun/magical-java-puzzle-pat-the-unicorns/

Unicorn.java

public class Unicorn {

	private static StackTraceElement[] previousTrace;

	public static boolean pat() {

		Throwable t = new Exception();
		StackTraceElement[] trace = t.getStackTrace();

		if (previousTrace == null) {
			previousTrace = trace;
			return true;
		}

		boolean newTrace = false;

		for (int i = 0; i < trace.length; i++) {
			if (!trace[i].equals(previousTrace[i])) {
				newTrace = true;
				break;
			}
		}

		if (newTrace) {
			previousTrace = trace;
		}

		return newTrace;
	}

}