A few of the "most credible reports":

<https://www.thetravel.com/most-credible-ufo-sightings/>

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How to weigh a pig:
1. Take a sturdy plank and carefully balance it on a sawhorse.
2. Tie the pig to one end of the plank.
3. Pile rocks of approximately the same size on the other end of the plank
   until it is evenly balanced.
4. Guess the weight of the rocks.