Have you ever known a dog to bite a power tool while it's running?

Yesterday I was using the weed whacker and Lizzie was barking at it for a while and then she bit the plastic guard while the weed whacker was still running. I turned it off immediately, of course, then put her inside so I could keep using the thing. It scared me half to death though.

Today I was using the chain saw and she started barking at it and it looked like she might be ready to take a bite at it too so I turned it off.

Is my dog insane?