Playing pranks on them
Spooking a cat with a cucumber might sound funny, but for the cat it's no joke. Even if their reaction seems exaggerated and absurd (it's just a cucumber, Mittens!), for them it means a lot to feel threatened in a space that they consider to be safe (your home, the area where they eat, etc).
According to some experts, cats' fear of cucumbers is due to them associating these vegetables with snakes, so their instinct kicks in and urges them to protect themselves.
So it's best to leave the cucumbers for your salad and not try to make a funny video at the expensive of your poor cat's peace of mind.