Sympatric speciation is the formation of two or more descendant species from a single ancestral species all occupying the same geographic location. Often-cited examples of sympatric speciation are found in insects that become dependent on different host plants in the same area.
Rice noodles are a type of semi-transparent pasta made from rice flour and water. Most are very long and thin, but you can also find flat rice noodles, as well. These noodles cook notably fast and can actually turn to mush if cooked for too long, so it's important to know how to cook them properly.
Vietnamese Beef Noodle Soup typically uses rice noodles. You can buy them dried or fresh. I love the slippery softness of fresh noodles (look in the refrigerator or freezer section.) Most restaurants will use dried, flat rice noodles. Look for ones that are medium thickness and flat like these.