On those days when Houston's summer refuses to end, when your eyes hurt from too much sunlight and your pores are clogged with sweat, when plastic objects melt on your dashboard, when you see squirrels spread-eagle on the ground, panting, and the neighborhood cats droop nearby, too languid to give chase -- on those days, you need a licuado. For those Mexican fruit smoothies, you should go to Nuo Leon, a neon-teal raspa hut on a bombed-out strip of Houston Avenue. All the varieties -- strawberry, cantaloupe, mango -- are concocted from real fruit, milk and shaved ice, and any one of them will restore both your electrolyte balance and your will to live. But be sure to order the smooth, sweet banana version ($3 for a large), which is topped with a whopping spoonful of cinnamon. That touch of mouth-warming spice complicates the cold, simple fruit drink, adding a touch of mystery and interest. Imagine: something you could rouse yourself to care about, in spite of the heat.