How to count to 9,999 with only four fingers on each of four paws.
Step 1: Look at the Cute Little Mouse Toes! (background)
I'm posting this to complement Kabukistar's instructable on counting methods.
Toe clipping is one of many methods of mouse-numbering used over the years in large lab colonies. The IACUC now recommends against toe clipping, instead preferring techniques that are less invasive and/or require lower levels of training. Properly clipped toes are easy to read, and make for unambiguous numbering. Even though you'll probably never need (or want) to clip a mouse's toes, the counting method is still of interest.
When you hold a mouse, they quite obligingly splay their toes for you to observe and count. (Because I don't keep rodents anymore, I found this nice picture on the internet.) They have four fingers and a thumb. This numbering method utilizes 1-2 fingers per paw, leaving the thumb intact for proper mouse motility.
Step 2: Scheme
The idea: toes are clipped to represent 0-9, with each foot representing a different power of ten.
Thus, the front right paw is the "ones paw", 1-9, (100); the front left paw is the "tens paw", 10-90, (101); the rear right paw is the "hundreds paw", 100-900, (102), and the rear left paw is the "thousands paw", 1000-9000 (103). Mix and match.
The mouse is held as shown, with splayed toes facing the reader. Toes are read left to right in all cases.
The following demonstration only uses the 1's and 10's paws (since I can't do much with my hindpaws) but hopefully you can extrapolate.
Step 3: Count to 9
Pictures of 1-9, using my fingers. Not clipped, otherwise I couldn't really show you all the numbers.
1-4 are obvious, right? Then you move onto combinations of two, walking along left to right. Follow along on your own fingers if the progression doesn't immediately make sense.
Step 4: Count by 10's
Same thing, left forepaw.
Step 5: Test
Roll over to check your answers.
Now use this technique to signal your friends across a room.