Two techniques. The first one is simply to set aside a low stab and return a stab of your own.
NOTE: a more recent, more elegant interpretation is shown here.
This is an impasse where we each performed the same technique. I don't know what the master wanted to explain with this, but my best guess is an admonition to not mirror attacks, so when you defended against a number 1 strike, respond with a number 2, not another number 1. This will avoid ending up in this position.