April 18, 2016 at 01:21AM

Today I Learned: 1) It turns out it's a bad sign if fish open their mouths a lot when breathing. Apparently it's something they only do if they're having difficulty getting enough oxygen, which happens normally after exercising or if frightened. If they do it *all the time*, it probably means their water is low in dissolved O2. This calls for a bubbler, more volume per fish, or potentially cooler water if the fish can tolerate it. Another sign of low oxygen -- if a fish spends an inordinate amount of time near the surface. 2) More good numbers to know: the smallest human cells, sperm, are about the size of a yeast cell -- between 4 and 6 micrometers across, with a volume of about 40 cubic micrometers. A HeLa cell*, in comparison, is something like 20-40 microns across and has a volume of around 1,000 cubic micrometers. Can you guess what the largest human cell is? I know you'll be tempted to just keep reading until you get to the answer, but I suggest you take a moment to stop and think about it before you hit the end of all this buffer text that's really supposed to keep your eyes off the answer until you've made a guess or two. Anyway. The answer is: the oocyte, or egg cell, which is a sphere something like 150 micrometers across, totalling 4 million cubic micrometers. * HeLa = a particularly famous immortalized cancer line used in research. HeLa cells are heavily mutated, but generically similar to skin cells. 3) More good numbers to know: less than two percent of terrorist attacks in Europe over the last five years. Most of the terrorist attacks in Europe are carried out with nationalist or political motivations, not religious ones. The numbers in the US are similar. Oh, another fun fact: In 2013, More people were killed in the US by toddlers than by terrorist attacks. Of course, that's only by one reckoning -- there are always differences in how "deaths by terrorist attacks" are defined. Also, 2013 was a pretty good year for the US in terms of deaths from terrorist attacks. But I hope the point is clear anyway. If you are motivated by fear of terrorist attack, please stop. There are many, many things that deserve your attention more. Terrorism is not a threat to your life in any meaningful sense, not if you live in the US or Europe*. * Unless you're, say, a Muslim in Europe right now. Then terrorism might, *might* show up on the list of things-likely-to-kill-you.