One would assume that Lucy and Ethel brought the three spare concrete slabs of footprints back to New York and displayed them prominently in their apartments; however, the slabs are never referenced or seen again after this episode.
John Wayne and William Frawley previously performed together in "Flame of the Barbary Coast" (1945).
As Fred walks in to the room rolling a cement slab of his version of John Wayne's footprints one of his lines is "now now now now. Don't touch it it's still wet". In order for him to say that Ethel has to appear to attempt to touch it. Here she has forgotten to do that so you can see when Lucy walks over she slightly lifts Ethel's right hand up towards the slab and now Fred can say his line.
John Wayne and William Frawley were also in The Fighting Seabees (1944)
Lucille Ball bumps Desi out of the way to deliver her line to John Wayne. She wanted to make sure she got it right on the first take.