속으로

In a sentence

• 나는 그 말을 듣고 속으로 크게 웃었다.

  I heard those words and laughed greatly inside.

  Here, '속으로' is used to express an action or state occurring internally or within one's thoughts or feelings, not outwardly visible.

• 속으로 생각하다가 답을 찾았다.

  I thought internally and found the answer.

  The use of '속으로' in this sentence specifies that the thinking process happens inwardly or privately.

• 그는 속으로 슬픔을 감추며 괜찮은 척했다.

  He hid his sadness inside and pretended to be okay.

  In this case, '속으로' indicates internal emotions or states that are not openly expressed.