Separated double object pronouns

Question

HI, I see this construction sometimes and very few info on it online. But sometimes two pronouns with two verbs in a sentence are separated with one before the first conjugated verb and other attached to the following infinitive verb. In my book for example - el pez numero catource-

1-- una vez la oí confesarle a Bernadette que tenía miedo de volver a equivocarse---

Why not, -- se la oí confesar ?

2-- Mi abuelo no contesta. Se limita a mirarlo con hostilidad.--

Why not: se lo limita a mirar?

What is this type of construction called?

Why separate them? Is this construction interchangeable with the traditional form of keeping pronouns together?

How common is it? I don't see it very often.

Thanks a lot

Answer

Hola Hola
This is a very interesting question and we've looked into it. 
The reason why you can't separate the pronouns in these specific cases is because each pronoun is part of each specific verb, so, for example:
la oí confesarle
la is only linked to oir: you hear [someone]
confesarle
le is only linked to confesar: you confess something to someone 
Also in:
Se limita a mirarlo
se limita a:   you have the verbal structure: limitarse a [hacer algo] with a meaning itself, it's all part of how this verb works, a pronominal verb
mirarlo: you look at someone; the object is only relevant to mirar, not to limitar
In other cases where you use both pronouns together, you have a different sort of structure, they are normally "perifrasis". Here is where you have that flexibility:
Se lo estoy poniendo -  Estoy poniéndoselo
Me lo va a mostrar -  Va a mostrármelo 
Se lo llevo diciendo hace rato -  Llevo diciéndoselo hace rato
Te las he vuelto a escribir -  He vuelto a escribírtelas
etc
Thanks for bringing this up. As I said, it's very interesting and we've noted it down for a possible informative article. 
Saludos cordiales
Inma

Answer

Thanks please let me know if you cover this topic. There is no information out there about it.