There is speculation that this could be Mouse and that NASA is keeping mum.
This microscopic imager mosaic taken by NASA’s Mars Exploration Rover Opportunity shows the rock dubbed “Diamond Jenness.” It was taken on sol 177 (July 23, 2004) after the rover first ground into the rock with its rock abrasion tool, or “Rat.” The rover later ground into the rock a second time. A sliced spherule, or “blueberry,” is visible in the upper left corner of the hole. Opportunity has bored nearly a dozen holes into the inner walls of “Endurance Crater.” On sols 177 and 178 (July 23 and July 24, 2004), the rover worked double-duty on Diamond Jenness. Surface debris and the bumpy shape of the rock resulted in a shallow and irregular hole, only about 2 millimeters (0.08 inch) deep. The final depth was not enough to remove all the bumps and leave a neat hole with a smooth floor. This extremely shallow depression was then examined by the rover’s alpha particle X-ray spectrometer.
Rat Hole in Mars?
“A friend emailed this in to me today and its really amazing and strange. I guess thats why I love this one so much. Its a cute rodent on Mars. Note it’s lighter color upper and lower eyelids, it’s nose and cheek areas, its ear, its front leg and stomach. Looks similar to a squirrel camouflaged in the stones and sand by its colors. Hey, who doesn’t love squirrels right? That doesn’t look like a squirrel you say? Then have a look at the photo below of similar squirrel in the same position on Earth. This might have been the big historical announcement that NASA was suppose to make, however they decided life on Mars was a secret worth keeping since they don’t want China or Russia to beat America to Mars. So they shut up about it and can take their time to Mars this way. The scientist jumped the gun and told the public about a major historical discovery on Mars…this must be what he was talking about. SCW’