What does this Rebus Picture mean?

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

The centre of the third figure is empty. What digit should fit inside?

Below, you can see some coding:
January = 1017
February = 628
March = 1335
April = 145
May = 1353
June = 1064
July = 1074
August = 186

Now deciphering the way it has been coded, can you find out how September will be coded?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?

Find out the number of circles in the given picture having Illusion

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

Cristina leaves home and then she makes exactly 3 left turns and returns home where she found 2 girls wearing the mask.

Who are these two masked girls?

I am a normal creature, but I have five hands. I can even have more but even then I will be considered normal.

Who am I?

Can you start the fire using two pieces of wood?