This simple piece fits perfectly into the rest of Picasso's work, which includes a large repertoire of simplified animal drawings with subjects ranging from common creatures like cats and sparrows to more exotic ones like ostriches.
These works are all done in black and white and aim to convey as much detail as possible with very little detail and very few lines. Picasso practiced drawing animals in this style from childhood, and by the time he had established himself as a proper artist he had honed these skills immensely.
The image is extremely simple, but in a way which communicates that simplicity was obviously the artist's intention; the purity of the image, which might otherwise look amateurish, instead is beautiful to behold.
Even with those other works as context, though, this one stands out as being especially simplistic. It almost more closely resembles a person's signature than an actual piece of artwork.
The entire image is composed of a single bold line, uncomplicated by any criss-crossed junctures or unnecessary extra flourishes. Instead, Picasso uses a contrast of smooth curves and sharp angles in order to define the shape of the mouse.
This is most clear in the head area of the mouse, where one can observe the way the wide, round ear tapers into the acute points of the snout and front feet. This is the part that forms the otherwise unremarkable squiggle that makes up the body and tail into a recognizable form.
The sketch's positioning is another interesting and unexpected feature of this piece. Rather than place the body of the mouse in the center of the canvas, as the viewer would typically expect, the mouse is a little higher within the frame, and its tail hangs down and mostly fills the center space instead.
This serves to emphasize how small the mouse really is (its own tail is at least as big as it is), but also to draw attention to the element of negative space in the piece.
The viewer's heightened awareness of just how much empty canvas surrounds the mouse drawing makes the single stroke of the image stand out that much more, and helps to define it as a representative shape despite the fact that it is not closed.
This picture makes the viewer's mind work a little more to fill in the gaps, making it particularly engaging to look at. It is also very easy to reproduce due to its simplicity, and it can blend into just about any space - these traits make it a very popular choice for reproductions.