This is an onion.

It is a perennial plant of order liliales family liliaceae genus allium with many thick leaves around the stem to store nutrients. The round bulb is used in cooking. It is nutritional and easy to grow and even grows in cold regions and doesn't spoil at room temperature, so it is cultivated and used in cooking all over the world. That's not what wikipedia says about the classification...

It's troublesome how when you slice an onion, you can't stop crying.

That's because when you cut it, the compound inside the onion which causes you to cry becomes a vapor and irritates your eyes and nose.

If you put something in your mouth, it's more difficult for tears to come out.

Really!?

Hih hrue, heahr harn't hahin hout!

*It's true, tears aren't coming out!

Putting something in your mouth causes salivation, which has priority, so it's harder for tears to come out. Other methods include sucking on something while cutting or cutting it while it's cold from the refrigerator.