Grampy Can Ya Hear Me is the fifth episode of Season 29.
Grampa gets a hearing aid and finally hears what everyone has been saying about him.
Meanwhile, Skinner discovers that his mother has been harboring the ultimate secret from him to find out.
Homer, Bart, Marge and Lisa are taking Grampa to the Springfield Planetarium for his 87th birthday. Homer uses his astronaut discount, but to do so, his diaper has to be checked, which has NASA written all over the waistband. Grampa complains about Homer being a cheapskate and pulls off his party hat in disgust, revealing his head to have changed to the shape of the hat. Homer tries to make an adjustment, but the hair just deflates like a balloon.
Inside, Homer steps on some scales which show his weight as being 182 pounds. Marge points out that this is Homer's weight on the moon, not his actual weight. Inside the planetarium show, Grampa complains about when the show is starting. Marge tells him it has started, but Grampa says it can't have started if he is still talking. Sideshow Mel tells Grampa to be quiet, as he can't hear about the Big Bang. The announcer states the Big Bang to have happened 13.8 billion years ago, to which Lisa lets out an audible gasp. A visual representation of the Big Bang exploding is shown on the screen, and Grampa runs out thinking that the theater has exploded and is on fire. The bright light rushes in to the theater and everyone is dazed because their eyes are adjusted to the darkness, and Moe was trying to develop film.
In the car, Grampa complains about the music not being loud enough, despite being ridiculously loud already. The family covers their ears, and turn it up some more. The volume control breaks, and the volume is stuck. As they arrive at the Springfield Retirement Castle to drop off Grampa, Marge wishes Grampa a happy birthday, to which Grampa says he never wants to hear those words again. Inside the retirement castle, the occupants are singing "Happy Birthday", much to Grampa's annoyance. One of the men asks Grampa to make a wish, shortly before collapsing. Grampa says that it "was a coincidence."
The Old Jewish Man meets Grampa in the hallway, and gives him a present, a hearing aid. Grampa says he doesn't want them, saying they will make him look old. The Old Jewish Man forces them into Grampa's ears, and immediately, Grampa can hear everything around him.
Lisa runs into Bart's bedroom before midnight and pulls back the covers, revealing a pillow decoy. Bart comes in the window, dressed as a ninja and holding Skinner's mailbox. Lisa confesses to him that the announcer in the planetarium said the universe was 13.8 billion years old, but on a test paper, she had put million. Bart, while putting a snake in Skinner's mailbox, asks what this has to do with him, to which Lisa asks if Bart was planning to break into the school soon. Despite not planning to break into the school for a month, Bart agrees.