What Invalidates Prayer
Urine or excretion, Janabah, menses.
One of the invalidating agents of prayer is to turn away from Qibla intentionally or forgetfully, or turning to right or left from Qibla or even turning intentionally so much that it is not towards Qibla in general view.
Whatever act that changes the appearance of prayer. For example, if a person moves his body voilently like a dancing or jumping, it invalidates prayer.
Uttering a word or words intentionally.
Intentional, loud and uncontrollable laugh.
If one intentionally weeps loudly over some worldly matters, his Prayer will be void. But if he weeps silently or loudly due to fear of Allah, or for the hereafter, there is no harm in it. In fact, it is among the best acts. It is said that the Lord of Martyrs, Imam Husain (a.s.) wept in his prayer when returning to hereafter.
Eating and drinking.
Folding hands (i.e. placing one hand on the other at prayer).
Saying “Amin” after Surah al-Hamd.