What's "in line" mean?

What does he mean by "the deep end"?

Here, "the deep end" has a couple of meanings. In the context of working at a swimming pool, "the deep end" is the part of the pool that is very deep, and you can't stand. As a phrase, if someone is "thrown into the deep end", it means they are in a completely new situation. They are not prepared, and they don't know what's going to happen. So for him, this is his first time as a lifeguard, so he's in "the deep end" as this is a new situation and challenge for him! Ex: I was thrown into the deep end when I said yes to helping with this project. I've never done coding before! Ex: I prefer the shallow side of the pool where I can stand rather than the deep end. Ex: When the company fired him, he wasn't afraid to jump into the deep end and start a new business.

Does "lust after someone" mean "have a crush on someone"? Or is it different?

The two expressions do have similar meanings! However, to "lust after/over someone" means to strongly desire or be sexually attracted to someone. Thus, it has a slightly different meaning than having a crush on someone, which has less of an emphasis on the physical aspect. Ex: My friend has been lusting over Leonardo DiCaprio for years. Ex: Stop lusting after her secretly and just go for it!

Can I use "can" instead of "could" here?

Generally when talking about possibility, which is what is happening here, while "could" and "can" have similar meanings they do have some different nuance. "Could" is usually used when there is small or weak possibility of something. While "can" is used for general facts or things that have a strong possibility. In this case, saying "a child could make them" is a little weaker and suggests that it's not very likely. Changing that with "can" would remove this nuance. Ex: It can be dangerous to cycle in the city. (Sounds like general fact) Ex: It could be dangerous to cycle in the city. (Sounds like a possibility)

What's "follow through" mean?

To "follow-through" means to start an action and actually finish it or produce the intended result. Ex: Kerry followed through on her offer and was able to get us a live band for the wedding! Ex: I struggle to follow through on the sewing projects I start.

Why does he say "four-hour" not "four-hours"? 🤔 How is it different?

When a number and unit of measurement are used together as adjectives, even if the unit number or number of objects is more than one, the adjective will be in the singular form. "Four" (4) is the number and "hour" is the measurement unit, which, when added together, become an adjective used to describe the makeup job. Remember that when numbers are used as adjectives in this way, the first two words need to be hyphenated. Ex: 1000-word novel. Ex: Six-foot tall tree. Ex: I worked a ten-hour shift today.