This is one of those cases where there are two hostas with the same name. One is registered and, therefore, the "official" version of H. 'Cat and Mouse' while the other is a non-registered plant and needs to be renamed to avoid further confusion.
 

This miniature size (3 inches high by 6 inches wide) hosta is a tissue culture sport of H. 'Blue Mouse Ears' which was registered by Hans Hansen and Shady Oaks Nursery of Minnesota in 2007 and given a U.S. patent in 2010. The chartreuse centered leaves get slightly lighter as the season progresses. It has pale purple flowers in July.

The Book of Little Hostas by Kathy and Michael Shadrack (2010) says: "It will be interesting to see if this plant gets bigger as it matures."

The New Encyclopedia of Hostas by Diana Grenfell (2009) states in its Miniature Hostas chapter: "The leaves retain the attractive variegation into early autumn. Slow to moderate growth rate...This delightful recent introduction is already captivating the collectors of mini hostas."

Hosta Helper will call this plant 'Cat and Mouse' (Hansen)
 

United States Patent: PP20862  (2010) Abstract: A new cultivar of hybrid Hosta named ‘Cat and Mouse’, characterized by its miniature plant size, its mounded plant habit, its round, glaucous leaves that are variegated with yellow-green center with blue-green margins in spring with the centers turning brighter and the margins turning greener in summer and its white flowers striped with lavender emerging in early summer on erect flower scapes.

2 8 2009 #7 2011 #9

Warren I. Pollock wrote comments about the many sports of H. 'Blue Mouse Ears' (which he termed BME) in The Hosta Journal (2012 Vol. 43 No. 2). He stated, "Shady Characters Nursery describes 'Cat and Mouse' leaves as 'chartreuse interior circled by an uneven blue-green margin. Lighter shades of green appear where the two colors overlap'. The center becomes much brighter and distinct later in the growing season. Also, the margin turns green later in the season. Furthermore, don't be surprised if your 'Cat and Mouse' is not stable, reverting to plain-leaved BME ."

Originated by Jocelyne Bastille of Aux Mille Hostas in Canada, this non-registered cultivar is of unidentified parentage. It is a miniature size hosta only about 2 inches high by 4 inches wide. The foliage is green with yellow to white marginal variegation.

Hosta Helper will call this plant 'Cat and Mouse' (Bastille)

The Hosta Journal (2012 Vol. 43 No 2) in an article by Warren I. Pollock (pg. 16) listed the following:

Blue Mouse Ears Series of Hostas