Dialogue interrupted by action/thought without a dialogue tag.
Characters can pause in their speech to do/think something and then resume the dialogue. When a dialogue tag isn’t used, special punctuation is required to set off the action and/or thought.

Enclose the first part of the dialogue in quotation marks but do not include the comma. Follow the ending quotation mark with an em dash, then the action and/or thought, and then another em dash. Resume the dialogue with another opening quotation mark, complete the dialogue, and end the dialogue with a period and a closing quotation mark. There are no spaces between the quotation marks and the dashes or between the dashes and the action and/or thought. (The spoken words are contained within the quotation marks and the action and/or thought is set off by the dashes.)

“He is leaving”—she turned on the stereo—”to get Ann’s gift.”

Dialogue abruptly cut off.
When dialogue is cut off—something suddenly diverts the character’s attention or another character interrupts him—use an em dash before the closing quotation mark. Dialogue can be interrupted mid-word or at the end of a word. Before deciding where to break the interrupted word, consider the sounds of words and syllables before deciding where to break the interrupted word.

“He is lea—”