Crossing a metal-grate bridge deck on a motorcycle in the rain can make the bike feel like it is squirming. The best response is to:

1. Brake hard before the grate to slow as much as possible
2. Stay in one lane position, hold the throttle steady, keep a firm but relaxed grip on the bars, and let the bike wander slightly under you
3. Lean aggressively to maintain grip
4. Switch lanes mid-bridge