In spoken English, you can add "I think" in the middle of a sentence to show that you're not completely sure about what you're saying.

It's, I think, the third time this happened.

A natural place to put "I think" is before a number:

My husband weighs, I think, 20 pounds more than me.

A less common place to put "I think" is before a verb:

He, I think, wanted us to find out about it.