If you didn't have a knife to slice open your watermelon, there are other tactics you could use. These include the smashing method, the sharp rock method and the rubber band method.
Yes, you read that last one correctly. If you wrap a certain number of rubber bands around a melon, you can create enough pressure on either side to actually crack it open.
The fellas on the "Slow Mo Guys" YouTube channel wanted to demonstrate just how this is done. Given that it ultimately took them about 500 rubber bands until the melon succumbed to the pressure -- a feat that took 20 minutes -- the team sped up that portion of the video. In the next frames, you can see the watermelon bulging at the top under the pressure of hundreds of bands around its middle. At this point, as they're trying to stretch the another rubber band over the now-oblong melon, it explodes.
Disregard the unlikely fact that you would have a few hundred rubber bands lying around and not a knife and just enjoy the 1,600 frame per second slow-mo action that captures the imminent explosion of not just one but a few watermelons (Warning: Some strong language):
Bonus: Did anyone else notice the instant rubber band ball that formed and flew off once the melons exploded?
The "Slow Mo Guys" explain how they could see liquid dripping out the sides of the watermelon before it "gave up." They then ponder if the same would happen to a human head. "Eventually," one of them responds.
(H/T: Daily Mail)