A mate I had years ago, owned a Blue Cattle dog called Fred that would only bite when you put the bike into gear.
You could mount the bike. It would sit there happy as Larry watching.
You could start it up, it'd wag its tail.
Put my helmet on, Fred couldn't care less.
you could rev it, no worries.
you pull in the clutch, it would slightly cock its head but but no dramas.
but as soon as you'd click it into first, whammo! it'd latch onto your calf
First time it happened I shut down the bike as I was in pain and got off.
My mate said he was terribly sorry but it wouldn't happen again, something just spooked him, he never normally bit anyone.
So I went through the same ritual, mount, start, helmet back on, clutch in, then... gear in and whammo! bugger latched back onto my leg!
I still always get nervous around Blue Heelers and motorbikes.