One thing at least is true about the name of this plant, the common mouse-ear (Cerastium fontanum); it is common! Debating which is the most common plant species is futile as it could never be established but f one were to try then surely common mouse-ear would be one of the main contenders. Being so common it is rarely given a second glance which is a shame.
Mouse-ears are members of the caryophyllaceae family which are better known as pinks; campions and stitchworts are related. The may be pinks but they are not all pink of course. My field guide lists eleven species of mouse-ears and they are have white flowers. They tend to be small plants, indeed, some are very small, and they have five deeply lobed petals making it seem that they may have ten petals in five pairs. Common mouse-ear is one of the larger plants in the group and is very variable in size and can grow to over a foot tall apparently but I have never seen any of this size. A ubiquitous plant of grasslands, especially where the rival vegetation is thin you can find in flower from April right through until November.
I have explained, I hope, why it is the common mouse-ear but where does the mouse-ear come from? It comes from the leaves that grow in opposite pairs at intervals along the stem. They are quite short, they are thin, they are pointed and they are hairy, just the ears of a long-tailed field mouse! Wikipedia describes the leaves as tear-shapped.