Garage Sale is the third part of the 12th episode of Dexter's Laboratory, which first aired on November 4, 2003. In this episode, Dexter creates an invention that turns people into hideous blobs. Mom then takes the invention and sells it at a garage sale, where the invention ends up in Mandark's hands.
Dexter builds a super dangerous and deadly machine that gets mistaken for a toy by Mom and ends up in a garage sale and gets sold to Mandark.
Dexter is in has lab working on another invention. He finishes it and it turns out to be a laser gun. He goes to test it out on a lab rat. He goes over to his case of lab rats and all of them are hiding in fear of him. He asks which one would like to be tested on and they all point to a stupid rat who is not scared at all. Dexter blasts the laser at him and it hits him offscreen. Dexter is in fear over what he is seeing and reacts as if what is happening is very disgusting and horrible. He says that that is a very horrible thing and that it was a good thing that he missed and hit a piece of lab equipment instead, but if that happened to a piece of lab equipment imagine what would happen if he did that to an actual living creature. He looks to go and find a place to hide it so that nobody will get their hands on it. He looks in many places but can't think of a perfect place to hide it.
He finally thinks of putting it out in the open in a pile of toys. Nobody would ever think to look there. Dexter leaves the room and then Mom comes in. She sees the pile of toys that the laser gun is in and she takes the toys away to the garage sale. Dexter comes back and realizes his laser gun is missing and he starts looking all over for it. He sees that garage sale and asks Dee Dee where it is. She says that she has no idea, but it might be here at the garage sale. Then, Dexter comes across Mandark who is about to buy the laser gun. Mandark is about to buy it and Dexter starts running toward him but Mandark buys it too soon and he just buys it before Dexter. Mandark goes off with the laser gun and goes home.
Dexter gets into the Robo Dexo 2000 and goes into Mandark's Lab looking for him. He doesn't see him in there anywhere until he hears his voice. Mandark is in his bathroom playing with the laser gun thinking of it as a toy submarine and he is playing with it in the tub. Dexter sneaks into his house and he goes over to the door. He breaks in and tells him to stop his evil plans. Mandark screams and has no idea what he's talking about. Dexter tells him thathe knows that it's a dangerous laser gun. When Mandark figures this out, he uses it to blast Dexter with it. Everything is happening to him offscreen and Mandark is having the same reaction as Dexter had. Then, it shows that Dexter is a green pile of goo. Mandark runs away laughing and Dexter starts chaising after him.