Expanded dice = Critical hits

When rolling your attack dice you may roll the highest result, for a d6 this would be a 6 of course. Once you roll this you can then roll an expanded dice up to 5 times, if each roll is the highest result. Each of these expanded dice will be counted as an additional hit. 

This means a basic unarmed punch can result in a total of 6 hits on a single attack, if luck is in your favor.