I have noticed a difference in receptivity to new fruits or veggies, determined by HOW I offer them. When I first offered banana, I held a piece by the edge, with part of it sticking out of my fingers, so the dog could easily grab it with his teeth. Yeah, he grabbed it, but immediately dropped it, and ate it reluctantly off the floor. I discovered, though, that if I place the piece of banana in the center of my palm and offer it with my hand flat, fingers closed (like you feed a horse a treat without getting fingers bitten off), then he gulped it down. This has remained my way of offering banana pieces - center palm, hand flat, fingers closed, or, similarly, I back hand it, when I'm facing away. I take a bite, then bite off a piece for the dog, offer it backhanded, he gulps it down, and so the cycle continues until the whole banana is gone.
Carrots are another story -- I can offer slices of those sticking straight out, and the devouring occurs in about two seconds. Watermelon gets the palm method. I guess the moisture factor (softness factor) somehow figures in.