Those things which render the Salaah invalid

Toes touching the ground in sajdah

Q: Majority of the time when I do sujood, my little toe doesn't touch the ground and perhaps the two besides it, but the big toe and one next to it  mostly do if not all do, so, is all toes touching the ground with pressure waajib/Fard, if so should one make movements in sujood or seating to ensure they touch the ground? Also I am not able to remember all the times this has happened, a lot though.

Laughing in Salaah

Q: I understand that if one laughs aloud in Salaah, his wudhu breaks, and if he laughs silently, only his Salaah breaks. However, I wish to know what constitutes a loud laugh and what constitutes laughing silently. Also, is a smile considered laughter?

Mazi coming out while one is leading the Salaah

Q: While leading the salaah, I had a feeling that mazi may have been discharged, but was not sure. When I returned home, I found a slight wetness
at the tip of my private area, and it was only when I began to clean it that the mazi began come out. Now I am uncertain if it remained in the passage 
during salaah and began to come out as a result of walking, or if any came out during salaah. Firstly, will it be necessary for the congregation to repeat the salaah? Secondly, is this common, or is it a medical issue?