Some Necessary Action may be taken while in Salah.  Following are some of the actions Compiled form the Practices and Incidents regardin the Prophet's Prayer:

• Crying, moaning, or groaning:

Crying, moaning, or groaning regardless of whether it is due to a fear of Allah or to any other reason (e.g., a moan due to some pain or injury that one cannot contain), is permissible.مُطرِّف بن عبد الله بن الشِّخِّير، عن أبيه، مُطرِّف بن عبد الله سَيِّدٌ جليل من ساداتْ التَّابعين، وأبُوهُ صحابي، يقولُ: رأيتُ رسُول الله -صلَّى الله عليه وسلَّم- يُصلِّي وفي صَدْرِهِ أَزِيزٌ كأزِيزِ المِرْجَلْ "I saw the Messenger of Allah praying and his chest was 'buzzing', like the buzzing of a cooking pot, due to crying." 

• Turning to a side due to some need

Abu Dawud records that when the Prophet صلَّى الله عليه وسلَّم prayed, he looked toward a valley because he had sent some horsemen to guard the valley.

• Killing a snake, scorpion or other harmful animals

Abu Hurairah reported that the Prophet صلَّى الله عليه وسلَّم said: "Kill the snake and the scorpion during the Salah."

• Taking a few steps due to some necessity 

'Aishah said: "The Messenger of Allah was offering Salah in the house and the door was locked. I came and knocked on the door and he walked over to open it for me and then he returned to his place of prayer. The door was in the direction of the Qiblah."

• Returning a Greeting by a motion 

'Abdullah ibn 'Umar says: "I asked Suhaib: 'How did the Messenger of Allah صلَّى الله عليه وسلَّم respond to the people when they greeted him while he was praying?' He said: 'He would signal to them with his hand.'"

• Saying Subhanallah and clapping 
• Praising Allah when one sneezes or recalls to mind a blessing 
• Correcting the Imam's mistake 
• Reciting from a copy of the Qur'an.

• Fidgeting with one's clothing or one's body unless there is some need to do so 
• Placing one's hands on hips during the prayer 
• Looking at something which distracts attention 
• Closing one's eyes . 
• Raising one's sight to the sky or upwards. 
• Performing the Salah while the food has been served.
• Motioning with both hands while making Tasleem.
• Praying when one needs to answer the call of nature.

He used to say: A man's prayer is cut off when there is nothing such as the end of a saddle in front of him, by: a [menstruating]55 woman, a donkey or a black dog. Abu Dharr said, 'I said: "O Messenger of Allaah, why the black dog rather than the red one?" He said, The black dog is a shaytaan.56

Piller : Arkan As-Salah (the essential components of the Salah)

Salah is invalid if any of these actions are missed during Salah. Missed actions can not compensated using prostrate for Sahw (forgetfulness). Salah Must be repeated to include the missing action.

Obligation : Wajibat As-Salah (the obligatory elements of the Salah)

Salah becomes invalid if any of these actions are are intentionally skipped during Salah. However,in case of forgetfulness Missed actions can be compensated using prostrate for Sahw (forgetfulness) and Salah must not be repeated if compensated using prostrate for Sahw.

Strongly Recommneded : Sunnan As-Salah (the recommended acts of the Salah)

Recommended actions in the Salah. Absence of these actions does not invalidate Salah, however they are highly recommended actions as they are evidnce for these actions being practiced by the prophet (صلى الله عليه وسلّم) . Actions in Salah based on evidences from teh practice of the prophet those are not Arkan (singular: Rukun) or Waajib.