Gee Whiz-z-z-z-z-z-z

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Introduction: The title card is shown as a billboard behind which Wile E. Coyote is hiding, ready to chase the Road Runner. He starts the chase, until he runs into a large truck. Wile E. runs the other way, and the truck shows the credit. The chase ends in a win for the truck, and the Coyote emerges battered. A box with director Chuck Jones' credit then squashes him. The Coyote throws the box away, and the shot freezes: COYOTE - Eatius Birdius. He resumes the chase, which freezes to show the Road Runner: Delicius-Delicius. The chase continues down the road until the Road Runner makes a U-turn. The Coyote turns around, then stops. The Road Runner completes the circuit around, meanwhile, and beeps as the Coyote turns around, causing him to leap back. The Road Runner starts off down the road and loosens it from its hinge briefly. Wile E. points worriedly and displays an "EGAD" sign, then an "!!" sign. He drops them and thinks of his new plan.
1. Wile E. hides in a manhole, and as the Road Runner passes over him, he pops out and fires a rifle. The bullet and the Road Runner are shown in slow time, with the bullet closing to within a half-body length of the bird. Then the Road Runner turns to notice the threat, lets out a beep and gears into super speed. The bullet then brakes in puzzlement and falls to the ground. Wile E. picks it up, and then it detonates. Behind another rock face (in completely different desert scenery), Wile E. paces until he comes up with a new plan.
2. Wile E. leaps out into the road with "1 sheet ACME Triple Strength BATTLESHIP STEEL ARMOR PLATE" in front of him; even this cannot stop the Road Runner from barreling through it. The Coyote stares in puzzlement at the resulting hole, which shows only the scenery behind him where parts of his body should logically be, then walks off the road in obvious distress at the massive trauma he evidently suffered.
3. While the Road Runner is feasting, the Coyote puts a lighted stick of dynamite on the end of a fishing line and casts it out. It lands next to the Road Runner, but then bounces and rolls underneath a large boulder, which causes the boulder to fly and ultimately drop on the Coyote.
4. Wile E. then puts on a Batman outfit and dives off a cliff. He finally gains traction just before falling onto some spikey rocks, and then flies in circles through the air. He continues to fly in a straight line, oblivious, until he smashes into a huge mountainside. The wings stick to the rock and the Coyote is left grappling in the air until he slams into the ground below. This scene was reused (with narration) in 1962's Adventures of the Road Runner.
5. The Coyote perches himself upon a high branch with an anvil attached to the end of an ACME rubber band. However, he cannot hold on long enough; his feet chafe on the branch, and he is slung directly into the ground with the anvil. Then, the band reactivates and lobs him directly up into the branch a second time.
6. Now, Wile E. attaches a dynamite stick to the end of a telescoping device in order to annihilate the Road Runner from afar. However, instead of launching the stick towards the Road Runner, the device knocks him backwards into a rock face. The dynamite is then pulled into the hole and detonates on the Coyote again.
7. Wile E. crafts a large "STOP! BRIDGE OUT" sign and then paints a landscape of a bridge being broken on a canvas (even though it does not match with the background). The Road Runner blasts through the corner of the canvas and continues through the road, while the Coyote emerges from his hiding place behind the sign, and suffers the effects of the painted landscape when he tries to run through it. This is a reversal of a usual gag, where the Road Runner can usually "jump into the painting", while Wile E. cannot.
8. The Coyote then mines a bridge with TNT, and expectantly waits behind the detonator. Unfortunately, the detonator fails to activate promptly, with the switch simply staying upright. Wile E. steps on, pulls, and slams the switch onto the ground before he runs onto the bridge to continue the chase. Not long after he does this, however, the controller finally activates and blows up the bridge with the Coyote still on it.
9. The Coyote crafts a makeshift jet bike from ACME Iron handle bars and an ACME jet motor, which launches without its owner (Powerhouse plays during the chase scene). Wile E. grabs at the end of it and manages to grope his way onto the jet bike. He keeps pace with the Road Runner around a mountain slope and up a cliff. It appears for a moment the bird is trapped. Then, however, the Road Runner repeats his earlier move and U-turns at the edge of the cliff, whereas the Coyote flies off it while trying to adjust his line to collide with his foe. (The vehicle smashes through the middle of the Runner's smoke cloud.) Still in midair, Wile E. turns the power off and looks back as the bike stops directly before reaching safety. The Road Runner is on this perch, and beeps to get his opponent's attention. Wile E. is obviously angry, but when the Road Runner points downwards, everything is silenced when Wile E. realizes he is about to suffer gravity once again. He loses his grip on the bike and plummets toward the earth. The embarrassed Coyote breaks the fourth wall by holding up a sign that asks, "How about ending this cartoon before I hit?" His wish is granted; as the iris begins to close, Wile E. holds up a second sign that says, "THANK YOU", and the cartoon fully ends.

Question: What failed to activate promptly?
Answer: The detonator