In New York, if you happen to take even a second to move (your car) forward after the traffic light turns green, the driver behind you honks at you immediately.
(c).
この島は、晴れていれば散歩や海水浴などが楽しめるが、雨に降られようものなら何もやることがなくなる。
On this island, you can have fun walking and swimming in the ocean on sunny days, but if it happens to rain, there's nothing to do.
The seats in this airplane have an extremely small amount of space between them, so if someone in the seat ahead chooses to lean back, large people like me are stuck (literally: are in a situation in which they literally cannot move).
The frequent visits of door-to-door salesmen these days are a real headache. The salesmen won't leave even if you say "no thanks," and if you happen to let them in the house by mistake, they won't leave until you buy (their products).
If you happen to go out on a motorcycle in pollen season (literally: pollen allergy season) by mistake, you'll keep sneezing and be miserable inside your full-face helmet.
(g).
この魚は猛毒を持っていて、間違ってそのトゲに刺されようものなら、患部が大きく腫れ上がってしまう。
This fish is very poisonous, and if you happen to be stung, that area will swell a lot.
Ms. Tamura has taken up (studying) Chinese medicine recently and if you ask her about it by mistake, you will end up listening to (her talk about) its effects for a full hour.