Spanish has two r sounds, one of which is called a flap, the other a trill. The rapid pronunciation of tt and dd in the English words Betty and ladder produces a sound similar to the Spanish flap r: the tongue touches the alveolar ridge (behind the upper teeth) once. Although English has no trill, when people imitate a motor, they often produce the Spanish trill r, which is a rapid series of flaps.
The trilled r is written rr between vowels (carro, correcto), and r at the beginning of a word (rico, rosa). Any other r is pronounced as a flap. Be careful to distinguish between the flap r and the trilled r. A mispronunciation will often change the meaning of a word–for example, pero (but) / perro (dog).
Subject: ¿Qué Tal?