Panel 1: We start things off with Mike and Martha continuing their marching down the mall.
Panel 2: Suddenly, the two of them notice something that alarms them.
Panel 3: The two of them detach from one another with such force, the muscles in their arms make a POIIIIIINNNNG!! noise from the recoil.
Panel 4: We switch back to the restaurant so that Connie can ask Elly if she thinks that they saw them.
Summary: The reason Mike clams up is that he's convinced that Elly will embarrass him so badly that even he thinks it best if he and Martha were to break up. What he never realized is that being revealed as being in the dark was so humiliating, she has to destroy what it is she didn't know about in order to look competent.