I don't let my cats have the toy mice, personal preference and if they play with feather toys it is supervised play only. I am leery not only of them getting foreign matter in their stomachs, but of the dyes used on some toys.
You can easily make a "safe' mouse for your cats. (this "pattern makes 20)
Cut about a 6" circle from a tightly woven piece of heavyweight fabric, Cut it in half. Fold each half in half and sew along the straight edge. Using a needle and thread sew in and out about 1/2 " down from the raw, rounded edge, stuff with cotton and pull the thread tight to gather up, tucking the raw edge inside, then stitch securly over the gathered up area with several stitches, pulling tight and knotting after each stitch. Of course this "mouse" has no tail, ears or eys etc...but the cats don`t know the difference and my cats are pretty rowdy with these mice and have never gotten one open yet. If they get too grubby looking I just make them some more. (The white fabric does`nt have any dyes.)
Linda