OK, here's another one I found, though this one is much less impressive simply because it's not as broad as a vegetable.
--snip--
DON'T scroll down too fast-do it slowly and follow the instructions below exactly, do the math in your head as fast as you can.
It may help to say the answers aloud quietly.
FOLLOW these instructions one at a time and as QUICKLY as you
can!
What is:
2+2?
4+4?
8+8?
16+16?
Quick! Pick a number between 12 and 5.
Got it?
Now scroll down...
>> >
The number you picked was 7, right?
--snip--
Ok, I admit my first thought was indeed 7... though when I said it outloud I said another number because I knew that going with your gut was how you fall into the trap. The explanation I saw on the page with this posted was because you're used to doing simple math and most people will immediately see 5 and 12 and think either 12-5 (7) or 12+5 (17).