1. If you err or forget something while reciting Al-Fatihah, you have to correct it because the prayer for the one who does not recite Al-Fatihah is invalid. 2. If you make a mistake when reciting the Surah after Al-Fatihah or you forget anything of it, it is not prescribed for you to say Istighfar; rather you should try to correct the mistake and remember what you forgot, but if you cannot do that then you may move on to the verse after it, or leave this Surah and start reciting another, or you may bow. If you do any of these things, there is nothing wrong with that.

If a man walks in front of the worshipper it does not interrupt his prayer, but it detracts from its reward. Animals passing in front of the praying person do not interrupt the prayer. The Sunnah indicates that the one who is praying should prevent anything or  anyone who wants to pass in front of him even if they are not one of those three, neither a dog nor a woman nor a donkey. It is Sunnah for the believer to put something in front of him before he prays, such as a chair or a spear that he sticks in the ground, or a wall or pillar that he faces towards when he is praying so that nothing will pass in front of him that could interrupt his prayer.