Are they jumping because they fear cucumbers or because something is suddenly there?
I think it’s because something is suddenly there, and they didn’t see how it got there. Cats are very observant of their surroundings - will all senses.
I’m going to test it tomorrow. My guess is that if you put a cucumber down on the floor while the cat watches you, he won’t care. One of mine will probably try to drag it somewhere; the other will just sniff at it and yawn.
-JT