As Killhammed Aiee shakes Chief Knockahomer, you briefly see Maggie jump up behind Homer's right arm. Yet when Bart opens up the robot, Maggie is mysteriously gone.
Milhouse evades sprinklers, dogs, etc. - only to get hit in face by Homer exiting the front door. It's the only time their front door open out instead of inwards.
When the bullies appear at the house to congratulate Bart on the robot, you can hear the doorbell and the door opening just as the bullies walk in.