There seems to be an issue with miss chance double-dipping on these types of abilities (Triple Snap, Flurry, etc.).
Basically, the game uses hit chance to determine how many hits you get with these types of abilities. The easiest way to see this is with Triple Snap -- try using Triple Snap after the Flayer uses his Focus buff and the results should be impressive. The other way is to use a Murloc or Mr Wiggles for their +hit buff, then swap to a pet with Flurry or Quills or etc.
Wowdb lists the hit chance for Flurry as 50%. I'm pretty sure this is just for the 2nd hit--it should do 1 hit guaranteed, then has a 50% chance to get a 2nd hit, and then it should get a 3rd hit if you go first. This is the first dip--it's just the baseline randomness of Flurry. When you get 1 fewer hit with Flurry due to this, the UI will not pop up a 'miss' text--the hits simply appear to never have happened. The big issue here is that the 50% chance for Flurry to get its extra hit is modified by the pet's hit chance, which is not 100%.
The second dip is the hit chance determination that every ability is subject to, and that I'm sure everyone is used to. When Flurry misses due to this, the UI will pop up a 'miss' text. The end result is that multi-hit abilities are doubly impacted by the pet's miss rate, which is not 0% even for equal-level opponents.
On a related note, there are multiple abilities that have a 25% chance to add a debuff when they hit--Frog Kiss, Sleeping Gas, Deep Freeze, Moth Dust, etc. This proc rate is also modified by hit chance, which you can see pretty dramatically if you use Lucky Dance and then swap in a pet with Frog Kiss or similar ability.