Look at the first three emails in the example below. Compare them with the fourth one. Here's why I clicked on that fourth email while ignoring others: It had suspense, drama, and some news that I believed had to do with me.

It is a natural human reflex to react to news. When you hear about a hurricane hitting a country or a terrorist attack or someone winning the Nobel prize, you switch on the news channel (or look it up on Twitter), because you want to find out everything about it. That's curiosity and man is a curious animal. If he weren't, we would still be sitting in a damp cave without fire.

But it is not only a man's psychological makeup that gets this kind of emails opened. Curiosity-inducing email subject lines are heralded as one of the best ways to boost email open rates by marketers. Alex Williams (creative director,  Trendline Interactive) developed a method for creating subject lines called the C.U.R.V.E. method, and the first element he talks about is curiosity. It's either that or freebies that get most of the emails opened.

Now let's look at some real examples of good subject lines that generate curiosity and understand why they work.

This subject line is bound to stop you in your tracks, make you look around to see if no one else is watching and then secretly open the email to find out. (Spoiler alert: The post doesn't answer this burning question, so no use going there.)

The about.me email uses curiosity in a very pleasant way. It has no shock value yet it piques your interest and you want to find out who is Amber and what's her story.

The second subject line is poorly executed. It tries to lure you in by keeping something secret and then changes its mind and tells you about it immediately, quite like a 4-year-old who can't keep his mouth shut. Also, it's incredibly long, but that's for another day.

Yet another example of a clever subject line that piques your interest:

BookMyShow: Two contrasting Fflms release this week

Instead of informing that xyz movies are releasing this week and be done with it, this email makes you wonder which movies are releasing and in what way they contrast.

Shopify emails take the C element of C.U.R.V.E a little too seriously. Like everything, even curiosity should be used in a measure. Too much curiosity and you stand the risk of coming across as clickbait-y.

Shopify Digest: How One Couple is Making $600,000 Per Year 
Shopify stories :  "There is nothing worse than..."

A lot of content marketers are A/B testing their headlines and the most common conclusion is that well thought out subject lines that pique people's interest work better than plain, drab subject lines.

Copy Hackers A/B tested their email lines and found that their intriguing subject line did better than another which had "un-fun words" like "comparative analysis." Here are both the headlines.

Option 1. Possibly the most overlooked home page opportunity in the universe...?
Option 2. Which home page kills it? A comparative analysis

The first subject line did 4.6 percent better than the second one. This means curiosity does boost your email open rates.

So every time a B2B marketer tells you that a subject line is good but it won't work for their business, tell them you have psychological studies, numbers and examples to prove.

Just be warned that you don't make the following mistakes.

With these mistakes averted, you are well on your way to create some of the best headlines and get phenomenal email open rates.

Published on: May 5, 2016
The opinions expressed here by Inc.com columnists are their own, not those of Inc.com.