Come, fluffy sponge, the image of true sheep
Shopping yesterday I saw this "doggy sponge":
Heh, cute. A sponge shaped like a "doggy." But then I saw the "Sheepy Sponge" beside it:
Note that these two sponges have distinct functions. The doggy sponge is for cleaning the sink. The sheepy sponge is for washing things "fluffy-gently but firmly" (モコモコやさしくしっかり). Their speech balloons reinforce this: the doggy sponge is saying "Pika[t]!", mimetic of a sudden glint of light, e.g. the reflection off a freshly-cleaned sink, and the sheepy sponge is saying "Moko[t]!", mimetic of... a sudden burst of fluffiness.
So, the sheepy sponge is not simply sheep-shaped. It also mimics the characteristics of a sheep. I submit therefore that one likely explanation of its name is not "sponge shaped like a sheep," but rather, "sheep-like sponge." It is not a "sheepy." It is sheepy.
Similarly, the doggy sponge's model is explicitly identified as the scottish terrier, known for its tough, wiry coat. Thus, the word "doggy" might be better understood as "doglike; canine" rather than "dog [dimun.]"
My suggested follow-up research program would focus on future products released by the same company. Product names using comparatives or superlatives ("doggier sponge," "cattiest tea-towel") would constitute evidence in support of my hypothesis, while names containing unambiguously nounal descriptors would be evidence in the other direction. Although they might pose entirely new interpretation problems as well: "parakeet drying tray," etc.
Marxy:
We have the sheepy sponge. I recommend it.