Present some details of one of your (most interesting) interaction diagrams. Interaction in this case means the way objects internal to your system interact with one another (by sending messages in the form of function calls) to complete an operation. It does NOT mean interaction between the system and an actor - that is the subject of a use case diagram, and you already presented one of those in Progress Report 3.
It would be most entertaining, and probably most informative to have more than one team member present the interaction together. Each speaker would represent a different object, and the speakers would alternate their responses as if they were executing the interaction, something like the following imaginary case:
Be sure to leave time for telling us your general progress, to-do items and problems as well.
Please do not include the interaction diagram in your written report. We can see that and much more in your Draft Project document. Just tell us your progress, to-do items, and problems as usual.
And remember to submit it to Gauchospace before the 6:30pm deadline.