Unfortunately you're probably done with the animation and presentation already. In the hopes this answer can help future questioners, however, this blog post has a walkthrough of steps that can loop a single slide as a sort of sub-presentation.
First, click Slide Show > Set Up Show.
Put a checkmark to Loop continuously until 'Esc'.
Click Ok. Now, Click Slide Show > Custom Shows. Click New.
Select the slide you are looping, click Add. Click Ok and Close.
Click on the slide you are looping. Click Slide Show > Slide Transition. Under Advance slide, put a checkmark to Automatically After. This will allow the slide to loop automatically. Do NOT Apply to all slides.
Right click on the thumbnail of the current slide, select Hide Slide.
Now, you will need to insert a new slide just before the slide you are looping. On the new slide, insert an action button. Set the hyperlink to the custom show you have created. Put a checkmark on "Show and Return"
This has worked for me.