I realize that it was the year 1997 when this article was written, but I thought of something that might be relevant.
If the spaghetti is dangling out of your mouth, every surface of the spaghetti is subject to air pressure. The end and all sides. The only side that is not subject to that pressure is the side inside your mouth. Specifically, the “side” that is exactly between where your mouth begins the suction. (In other words, it really doesn’t matter how much of the spaghetti is inside your mouth, just as long as it crosses the point between high air pressure (outside your mouth) and low air pressure (inside your mouth))
Since this is the case, the pressure on the end outside your mouth, pushes the spaghetti in; but it does not buckle it. After all, the same amount of pressure that is exerted on the end, is also exerted on the sides. (in fact, there is probably more pressure on the sides that there is on the end, because there is more surface area)
Thus, the spaghetti moves from outside to inside.
But then we run into another problem. Let’s say that I am enjoying a spaghetti dinner with a loved one, and she ends up with the other end of the spaghetti strand that I’m trying to slurp. There would be no “end” for the air to push. Would it be possible to slurp in such a situation? Perhaps there’s another variable to consider here. Maybe the pressure on the side of the spaghetti strand would be enough to pressure it in.
-Ducc