Carrion swarm has an interrupt baked into it as well as the (unglyphed) knockback.Yeah they kind of are. There's shadowfury, but reticles aren't the most convenient thing sometimes.
The only decent tank pet for locks doesn't do interrupts. You will have to tank the mob if you want your pet to be alive to interrupt.
Knockbacks don't reset ability cooldowns so don't even bother with carrion swarm because the mob will just start casting it again.
So yup you get stuck with shadowfury. It's not what I would like and 30 sec is a little longer than desirable but I'm okay with it.
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What is bizarre is putting things out in the world that can't (reasonably) be killed without an interrupt, and linking achievements to them.
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I'm actually a little surprised they didn't put a 20s interrupt doodad that doesn't need to be equipped as loot on one of the Pandaria rares.