There is a moment in the movie when the hero (Zach Galligan) blinds Gizmo with some light, and Gizmo falls and is hurt. Then the boy takes Gizmo to the bathroom to cure the wound.

When he enters the bathroom, do not focus on the boy carrying Gizmo but the lower right zone of your screen, you'll see the two ears of the animatronic of Gizmo which will replace the one the boy is carrying.

WARNING: I think this can only be seen on widescreen version, because the pan and scan one must have cut this!