Fleas for Excuses

Austin from Austin. By reading on I might have found from Austin himself the answer to my question about diminishing fleas. See this passage from "A Plea for Excuses":

For this problem too the field of Excuses is a fruitful one. Here is a matter both contentious and practically important for everybody, so that ordinary language is on its toes: yet also, on its back it has long had a bigger flea to bite it, in the shape of the Law, and both again have lately attracted the attention of yet another, and at least a healthily growing, flea, in the shape of psychology.

A strange passage, perhaps, because Austin doesn't usually recycle clever images; and "on its toes"/"on its back" is particularly infelicitous. In this case, his words don't do much for me.