Good Riddles

Question: An item looks square from outside, Circle when opened and Triangle when taken out.

Question: Two cops walk into a doughnut shop. One gets a sprinkle doughnut and the second one gets a sugar doughnut. What did the third cop get?

Question: At the sound of me, men may dream, or they may stamp their feet.
At the sound of me, women may laugh, or even weep.

What am I?

Question: How can a pants pocket be empty but still have something in it?

Question: What type of monkey only howls?