multiple slave processes on slave machine

[Scott Bartram]

I have a master and multiple slave machines.  The slaves are configured to start via ssh from the master.  Initially, there is a single java process running the slave.jar.  Occasionally, I'll login to a slave and find that there are 2 or even sometimes 3 java processes running slave.jar.  This is while no jobs are running.

How many slave processes should be running when the slave is idle?