My definition of a mouse is a player who is passive and who likes to minibet and miniraise. A mouse may or may not be a loose caller but he/she should be quite readable.

Yesterday I sat at a NL25 table and saw some player min. bet all 3 streets with a set.

Another hand, a player in BB flopped quads with 33 on a board of 33AQJ, the action went checked through on flop, check-called a min bet from UTG who had AK and was a mouse himself, and then checked through again on the river again.

Because of their predictability mice are easily for us to avoid losing huge pots to, unlike a LAG and the associated variances that we might have deal with.

The question is, where do we rank the mice between the stations and the wild donks?