We mastered Magic Eye books as kids, so we're game for a good optical illusion.

But still, we were thrown at the Greenmarket by what appeared to be a basket of miniature watermelons, each the size of the last joint of your thumb. But their sign read "cucumbers."

These whimsically shaped, diminutive cukes are unlike any fruit we've seen. Called Mexican sour gherkins or West Indian gherkins, their size belies their flavor: Slightly sour, they taste green and wild. With a thick crunchy skin, they also don't suffer from watery interiors like their larger supermarket cousins.

While you wouldn't be remiss to eat them raw by the handful, these gherkins are superb in a myriad of dishes.

Briefly boil them in water, vinegar, salt and sugar for a quick pickle. Add them to a cocktail for a savory garnish or toss them in a salad of soft cheese, arugula and sliced beets to add texture and that eye-popping color.

Like regular cucumbers, the gherkins are best in the height of summer. They appear around July and will last only a few more weeks as the growing season wanes and cooler temperatures approach.

Mexican sour gherkins are available at the Windfall Farms stand at the Union Square Greenmarket (Wed. and Sat., 8 a.m. to 6 p.m.).