Some Spanish verbs have irregular present participle forms when used in the present progressive tense. For stem-changing -ir verbs, the e changes to i and o changes to u. For -er verbs like creer, leer, traer, and oir, the i changes to y in the -iendo ending. Examples of irregular present participles are diciendo, pidiendo, repitiendo, siguiendo, sirviendo, vistiendo, and durmiendo.