Irregular Present Progressive Gerunds

As you know, a gerund is affixed to a present progressive to form the Spanish equivalent of the English "-ing". There are some irregular gerund formations, which usually occur in verbs like caer("to fall") and leer("to read"). A "y" is injected in the word to avoid a clumping of vowels, and allows easier pronunciation:

leer leyendo
Manuel está leyendo su revista.
Manuel is reading his magazine.

caer cayendo
Estoy cayendo.
I am falling.

Other verbs that follow this pattern are traer("to bring"), poseer("to possess"), and oír("to hear").

Also, the -ir verbs that are irregular in the preterit third-person also carry forth the same irregularity into the gerund formation. Note the following chart of examples:

Verb	Preterit Form	Gerund
dormir	durmió	durmiendo
morir	murió	muriendo
pedir	pidió	pidiendo
repetir	repitió	repitiendo
sentir	sintió	sintiendo
servir	sirvió	sirviendo

If you didn't have enough to worry about, there are also a couple of other irregularities that stand alone. The verbs poder("to be able to") and ir("to go") have as their gerunds pudiendo and yendo, respectively. Also, the two verbs venir("to come") and decir("to say, to tell") exhibit irregular gerunds:

decir	diciendo
venir	viniendo