They taste like a cucumber, but look like an apple. Only they don't look that much like an apple. They are: apple cucumbers.
I found these in the markets the other day and had to buy one. On first bite I was disappointed that they didn't taste like apples with the texture of cucumber, but that's my own fault for not buying cucumber apples. Compared with their elongated counterparts they were slightly lacking in flavour and had tougher skins, but it's possible that I was sold an immature or low-quality piece of fruit. That's the risk you run buying exotic produce: the consumer is unfamiliar and will tend to buy on novelty alone, so there's not as much incentive to be pedantic about quality.
Still, it was good to be able to cross 'apple cucumber' off my list of 'Cucumbers to eat before I die', and sliced thinly it fit right in with smoked salmon, dijon mustard, and cracker pepper for lunch.
(A post where I review a cucumber — try finding that kind of toe-curling excitement at any other food blog!)