Islamic Way of Slaughtering Is the Perfect Way
17-3-2019 | IslamWeb
Question:
1)why not allowed sacrifice of animal in one hit of knife from back side of neck?2) sometimes Hindus are asking why prophet marry to very young girl Ayesha (R.A). how to justify it kindly explain ?
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
Perhaps it is more appropriate to start with clarifying the Islamic way of slaughtering an animal. This is done by cutting off the two jugular veins, the throat, and the gullet; there is some difference of opinion among the scholars about some details.
For more benefit, please refer to Fataawa 127050 and 89723.
Among the merits of this Islamic way of slaughtering is that the animal dies fast, which is something required to save the animal
From suffering. This kindness to the animal during slaughtering is something enjoined by the wise Sharee’ah.
Shaddaad ibn Aws 
narrated that the Prophet said: “Allah prescribed kindness in everything, so if you want to kill (anyone for some justified reason), kill (him/her) humanely (in a perfect and kind manner), and when you slaughter (an animal), slaughter (it) in a good way; you should sharpen the blade to make the slaughtered animal die comfortably.” [Muslim]
The second purpose intended by slaughtering in this way is to make all the blood flow out of the animal, which is very useful as experts in veterinary medicine stated. They said that making all the blood flow out of the animal by slaughtering purifies it from germs. The purpose of slaughtering is to make the largest amount of blood flow out of the animal, which increases the efficiency and taste of the meat and reduces harmful bacterial growth. If the blood does not come out of the animal and is congested in the body, then this causes much harm.
As for slaughtering the animal by one strike of the knife from back side of neck, then this is not considered as Islamic slaughtering, and it does not fulfill the abovementioned purposes. What is slaughtered in this way is considered to be dead meat and it is not permissible to eat it.
There is an issue which the jurists discussed: if we slaughter the animal from the back of the neck, whether deliberately or being forced to do so, and the knife cuts the things that should be cut when slaughtering (as mentioned above), does this make the slaughtered animal lawful or not? There are some details about this which Ibn Qudaamah 
mentioned in his book Al-Mughni. But in any case, it is better to abide by Islamic way of slaughtering.
This is in regard to your first question.
As regards your second question concerning the marriage of the Prophet to 'Aa'ishah 
at a young age, then this is a misconception which we were asked many times, and we have already answered it in many Fataawa. In this regard please refer to Fataawa at her marriage">191627, 8218, ">84343, and 18970.
Allah knows best.