Douglas Fear from San Jose, Calif. stumbled onto this mouse pattern on accident while tying a topwater burbler for bass. Pretty soon he tweaked his pattern and came up with the mouse you see here.
He uses 2mm craft foam on a size 4 Mustad hook. He also uses thick thread that doesn't cut the foam. I'm going to take one up to Alaska this May and see if they work on those rainbows as well as they do on California bass.