Observe dmg when Hissy attacks without any ability and with Sic' Em. First two times it attacks without the ability and deals 228.
Third and fourth time attacks with Sic' Em and deals 150 + trauma dmg over time (special ability) + clean 228/231 again.

Sic'Em is supposed to be + 40 dmg + special ability.
Hissy's special ability is - Trauma dmg over time 25/sec
Trauma is ineffective against corpse.

It's supposed to deal Slashing or Crushing which should be similar to when no ability is used + 40 + Trauma over Time.
It would seem that using the ability actually changes the base attack to trauma which is ineffective against the corpse. Making the pet weaker than when using no ability at all. In my opinion the base dmg type should not be change (if indeed this is what causes the dmg to drop so much) and it should not make the pet weaker.

I may be wrong though. Trying to diagnose dmg like this is not an exact science