How to format cells from one column which match cells from another column

[Legacy 362812]

Hi, I'm trying to compare two columns worth of data. I'd like to use conditional formatting (I think?) to compare cells in column A with cells in column B and highlight the matching cells if/when any cell in column A matches any cell in column B. For example:
[TABLE="class: grid, width: 300"]
<tbody>[TR]
[TD]Sparrow[/TD]
[TD]Eagle[/TD]
[/TR]
[TR]
[TD]Thrush[/TD]
[TD]Falcon[/TD]
[/TR]
[TR]
[TD]Warbler[/TD]
[TD]Thrush[/TD]
[/TR]
[TR]
[TD]Robin[/TD]
[TD]Crow[/TD]
[/TR]
[TR]
[TD]Swallow[/TD]
[TD]Warbler[/TD]
[/TR]
</tbody>[/TABLE]

How would I go about doing that? The cells contain text strings which may or may not include punctuation, etc. I'm running Excel 2015 on a mac. Thanks in advance for any advice you have!

 

[Joe4]

Let's say that your data exists in cells A2:B100.

To highlight the column A entries:
- Highlight cells A2:A100 and then use this Conditional Formatting formula:
=COUNTIF(B$2:B$100,A2)
- choose your red text color formatting option

To highlight the column B entries:
- Highlight cells B2:B100 and then use this Conditional Formatting formula:
=COUNTIF(A$2:A$100,B2)
- choose your red text color formatting option

 

[Legacy 362812]

Thanks @Joe4. Hmm, I've got this working (cells are getting colored), but it's not quite working the way I'd expect. For example, I've got something like "President Lincoln" in A:24 and the same string, "President Lincoln" in B:14, but they're not lighting up. The ones that are lighting up don't quite make sense (I don't see the duplicate in the other column). Maybe it would make more sense to highlight the entire field and create a conditional format that checks for and marks duplicates. How would I go about doing that?

 

[Legacy 362812]

I solved this with something I learned is more basic and native to Excel. This image describes it. Here are the steps:
1. Select the cells you want to compare.
2. Home Tab > Conditional Formatting > Highlight Cells Rules > Duplicate Values.