reptilian rats

While I commend this student for knowing about reptiles I question how they have managed to reach the second prac of their rat dissection. Unfortuntely I was not present until after this question was posed! I hope the student just has a strange sense of humour!
Student: (looking at the rat heart) So this has a three chambered heart right?
TA: No it has four.
Student: But why? Its a reptile.