Crit- chances are are purely some % base calculation like every hit you had like 10 % chance of crit like that..
My observations till now - every 100 kiss (.1 / 1 energy) gives like minimum 4 crits or 8-9 crits at best
Every 100 feather (.2 / 2 energy) gives like minimum 4 crits or 7-8 crits at best
So you can say that there is around 5 % chance of crit at least .
I think there is no pattern as i already tried that too (For first 50 energy use for .2 / 2 energy I got '0' crits but later 70 energy use I got 6 crits)
Best of Luck finding some clue to pattern