Can You Figure This Out?

Here is a riddle:

Railroad crossing, watch out for the cars. Can you spell it without any "r"s?

What is wrong with this paragraph?

How quickly can you find out what is unusual about this paragraph? It looks so ordinary that you would think that nothing was wrong with it at all; and in fact, nothing is. But it is unusual. Why? If you study it and think about it you may find out, but I am not going to assist you in any way. You must do it without coaching. No doubt if you work at it for long, it will dawn on you. I don't know. Now, go to work and try your luck.

This puzzle is courtesy of the Klutz The Encyclopedia of Immaturity. 

Dancing Robots

Hypnotizing, isn't it?

The Ghost Train

A Day In the Life of A Lego Man

A Riddle!

Here is a riddle that my friend told me. I couldn't figure it out, and when he told me what the answer was, I said, "Aww! I can't believe I didn't get that!" Here it is...

A man is walking in a forest when he comes across a black box. He wants to know what is in it, so he tries to open it. He can't because there is no latch or opening. He happens to have a sledgehammer, so he hits it with the sledgehammer. It doesn't break. He shakes the box and listens for anything. He doesn't hear anything. He smells the box. It doesn't smell like anything. Then, he IMMEDIATELY KNOWS what is in the box. HOW AND WHY DOES HE KNOW WHAT IS IN THE BOX?
-It is indestructible
-It is smell-proof
-It is sound-proof
-There is something in the box
-In the box, there is air, but something else
You may ask yes or no questions.