July 19, 2016 at 01:04AM

Today I Learned: 1) Today I learned how stomachs get their HCl and enzymes! Yesterday I did not know, but I put the question to the AskScience subreddit, and they delivered! The lining of the stomach is covered in little pores called gastric pits, which are basically infolded pockets of the innermost cell layer (there are some nice basic diagrams here, along with tons of terminology and other information if you're interested: http://ift.tt/2a54TUq). The cells in these pockets secrete a mix of HCl and an inactive protease* called pepsinogen. Under highly acidic conditions, pepsinogen breaks down into pepsin, which is an *active* protease. This way, the cells of the stomach can produce protease safely, without it turning on and shredding the cell from the inside out, and the stomach will naturally convert that into an active protease. The tricky bit is that the lining of the stomach, including the pores, is covered by a layer of mucus that keeps the stomach from digesting itself. How does the acid/protease mix get through the mucus layer, if the whole point of the mucus layer is to stop acid and enzymes from getting past it? The answer is that the gastric pores occasionally contract strongly, pushing the aqueous acid/protease mix into the mucus. It cuts a channel through the mucus and blasts through to the other side. The hole in the mucus heals pretty quickly, and then there's nothing to force the juice back through. The principle behind this was apparently only discovered in the early 90s, as evidenced by this paper (paywall warning): http://ift.tt/2a6ExnI. *protease == a protein that breaks down proteins. 2) I've noticed that my mantis will sometimes bob back and forth when it spots me. I figured it was gaguing its distance to me so it could figure out whether I was predator or prey. Today I learned that the purpose of a mantis's rangefinding isn't to figure out whether you are dangerous or not -- it's to figure out whether it can jump onto you or not. 3) Ikea makes (or possibly made) a rather ingeneious new version of a screw, called a wheel lock: http://ift.tt/2a54HnW. The wheel lock goes into a cylindrical inset in a flat piece of material, with the flat face flush with the face of whatever it's embedded in. A hole in the side of the embedding material lets a pretty standard screw through, which makes contact with the rounded side of the wheel lock. By screwing the wheel lock, you screw the screw into the *side* of the wheel lock, drawing it into place! I didn't know there were novel forms of screw to discover out there -- thanks for making my day, IKEA!