Cells from a woolly mammoth that died 28,000 years ago have begun to show “signs of biological [activity]” after they were implanted in mouse cells. However, researchers caution that it’s unlikely the extinct creatures will walk the Earth again anytime soon.

The research, published in Scientific Reports, details how a well-preserved woolly mammoth, found in 2011 in the Siberian permafrost, has begun to show some activity.