I use the chisanbop system to count on my fingers up to 99. I've seen demonstrations of children doing multiplication and division using it, but I haven't taken the time to learn it.

Non-cartoon rabbits have 5 digits ( Watership Down's numbering system - 5 or greater = thousands (hrair) http://en.wikipedia.org/wiki/The_Magical_Number_Seven,_Plus_or_Minus_Two ).

I assume that like other canines, foxes have 4 toes and a dew claw.