Dan Grayson makes a phone call from a restaurant called "Clem's Café." This is probably a nod to the production manager of the series, Clem Beauchamp.
When the blackmailer and Clark Kent meet in the booth at Clem's Café, the blackmailer continues his motif of cracking walnuts with his bare hands. Behind Kent on the wall is an advertisement for ice cream. The flavor featured on the ad is black walnut.