What does this simple rebus mean?

It's a test that will check your IQ.

Suppose you have one 11 minute hourglass and one 13 minute hourglass.

Can you measure exactly fifteen minutes using them ?

Things are just as they seem, right? Well, check again.
Can you count the number of tigers in this picture ?

Spot the cat in the picture below

Rebus Puzzle Definition: A rebus is an illusion device that uses pictures to represent words or parts of words.
What does This Rebus Puzzle Identify?

Why Aeroplane windows are round?

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

why number 8549176320 is one of a kind?

A brand new Mobile Phone was on sale at 20% as a promotional offer. By what per cent must the Mobile price be increased to sell it at the original price again?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?