Unix piping - echo and cat

Question

I am having trouble with the following command in Unix Bash Shell:

echo "This is some text" | cat dashes - dashes

"dashes" is a file containing the line of text: "---------------------------------"

From my understanding, the left command's stout stream becomes the right commands stdin stream. What I expected to be printed was:

This is some text
---------------------------------

But what actually printed was this:

---------------------------------
This is some text
---------------------------------

---

So I have two questions:

1. What is happening when the echo pipes into the cat, to make the given output?

2. How does the " - dashes" at end of the command work?

Answer 1

This is expected because - in between 2 file names means print all the data from stdin . Take this example:

date | cat dashes - dashes
---------------------------------
Fri May 29 05:49:05 EDT 2015
---------------------------------