I was talking to a banker friend sometime in June this year, and I mentioned that I couldn't come to the bank because "it was raining cat and dog outside". He laughed and said, it is a literal word, it isn't like it is dropping cats and dogs or any other animal, just get on your raincoat and an umbrella, and find your way to bank. While the word raining cat and dog can be a literal word, animals actually fall from the sky sometimes.
These phenomena are rare but they actually but history has shown that they did happen like in 1555 when it rained fish or in 1680 when it was raining snake during the Renaissance storm. Some of these documented experience looked over exaggerated but the documentation showed that it did happen but in recent times, we have had our own experiences that we documented properly.
You do not believe what I wrote above and if you are skeptical, it is understandable but in recent times we had that experience again when Frogs fell in their thousands in Serbia in the year 2005. But that's just one experience, and you cannot say for sure that they really saw frogs. well, in 2009, thousands of Tadpoles fell with rain in Japan also in 2010, fishes fell in the Northern territory of Australia for several days and they were still alive. Some other countries that have had fishy rain experience are India, the Philippines, Ethiopia, Mexico, Sri Lanka, Honduras, and Wales.
Some rains might be astonishing while others freaking like the Spider rain in Australia in 2015. Scientist said it was a case of ballooning where infant spiders floated with their silk in the air current, and it fell with the rain. Scientists could give explanation for the flying animals that falls but it becomes a little complicated when aquatic animals are involved.
For the aquatic animals, scientist believe that they got up there through waterspouts of tornadoes over open waters like lakes, and seas and are formed in fair weather or when land tornadoes move to sea although this phenomenon is quite uncommon. This is just a theory and in the case of occasional events of rainfall that comes with small aquatic animals in areas far from water, it could be explained by land tornadoes.
Although the waterspout idea looks like a better explanation, scientists haven't been able to monitor these events properly as they occur in rare occasions. Also, scientist think that the reason why in recent times we have been able to see small fishes or frogs and not other water inhabitants fall from the sky from waterspouts is associated with size and weight but this thought is still being debated as we will agree that there are smaller animals in water compared to fishes and frogs.
Since we are not able to see when spout pick up animals, it is difficult to explain this phenomenon currently but for now, if you see frogs or small fishes falling from the sky, it isn't a sign that the world is coming to an end like most people will say, it is just a rare weather phenomenon with reasonable explanation by scientist. I will also be in the lookout for animals fall from the sky but for now I haven't had the personal experience although I have seen rain falling ice.
https://www.researchgate.net/figure/Left-Raining-snakes-during-a-Renaissance
https://www.theguardian.com/world/video/2015/may
https://www.telegraph.co.uk/news/newstopics/howaboutthat
https://www.huffingtonpost.co.uk/2015/05/18/spiders-rain-australian
https://www.livescience.com/44760-raining-frogs.html
https://www.smithsonianmag.com/science-nature/strange-rain
https://www.weather.gov/apx/waterspout
https://spo.nmfs.noaa.gov/Fishery%20Leaflets/leaflet513.pdf
https://oceantoday.noaa.gov/waterspouts/