If untrimmed, a cat's nail might snag on one of those mats...my concern would be if the snag pulled the yarn (I think it would depend how tightly the piece is made?) once it snagged. Cats do tend to like to chew/potentially swallow strings...so as a caution I'd ask the shelter what they think. Really awesome of you to want to help them! I worked with a few rescues who loved the cotton/polar fleece mini-quilts they got as donations...very special!