this is an easy experiment, but it can only proofed one way or the other, with a large number of experiments.
scenario:
you spot a grasshopper or similar plant pest, and try to catch it, so it doesn't eat your beloved plant.
the idea:
many grasshoppers and alike, start to wiggle a bit once they seem to detect a thread. the idea is to in 50% of the cases, to try to catch the insect with a straight forward hand movement, but in the other 50%, to as well, wiggle or move your hand side to side or so forth, till you close enough to attempt the catch. maybe even wiggling the whole body would help as well.
the hypothesis:
the insect uses wiggling and side movements, to evade capture. it thinks wiggling is a cloaking device! maybe this strength, is also it's weakness and it does not notice (or see it as danger) if an object wiggles.
I got a few results already...
branches and leaves move often, it would be stress full for the insect to, take flight every time a branch moves or a leave(s) casts a shadow.