So, no mental events are physical events. Try to use the visualization method to determine whether or not the argument is valid. If mental and physical events aren't your thing, then use the counterexample method as outlined in class. Be sure to create your own counterexample. No cats are otters.
All otters are animals.
Therefore, no cats are animals. In the counterexample, we start with true premises, but end up with a false conclusion. And for our purposes, an invalid argument form indicates that the original argument it was based on, is also invalid.