This a multi-role joke:
Huntingdon Life Sciences (the notorious laboratory for testing stuff on animals, which will be more or less familiar depending on how near you are to the A1) has stopped using rats in their labs.
Instead they are now using [insert appropriate unit, branch, regiment etc etc]. There were 3 reasons for this:
1. The lab assistants were becoming too fond of the rats.
2. There aren't enough rats.
3. There are some things even rats won't do.
Rgds SOS
P.S. there was quite a lot of good material in response to your last thread, you can't have used it all can you?
Rgds SOS