In English we use "on a second thought" to express that we're thinking again about a previously made choice. I've seen this expression in a comment to this post, A word whose meaning is "one whose diet includes fish but no other meat", and I wondered how to express that in Italian.
Another example: we can say, "You know, on a second thought, I think I'll go to watch that film" if we previously decided not to watch it.
How can we say a similar expression in Italian?