By the way,

I'm in fifth grade and I need to find the meaning and origin of this phrase. Can you please help me? Thanks,
Sax

Hi Sax. The phrase "call your bluff" comes from poker, a card game.
Here's a definition of "bluff":
bluff1
v. bluffed, bluff·ing, bluffs
v. tr.
To mislead or deceive.
To impress, deter, or intimidate by a false display of confidence.
Games To try to mislead (opponents) in a card game by heavy betting on a poor hand or by little or no betting on a good one.
v. intr.
To engage in a false display of strength or confidence.
n.
The act or practice of bluffing.
One that bluffs.
--
[Probably from Dutch bluffen, from Low German.]
--
bluffa·ble adj.
bluffer n.
--
The American Heritage® Dictionary of the English Language, Fourth Edition. Copyright © 2000 by Houghton Mifflin Company. Published by the Houghton Mifflin Company. All rights reserved.

"Call" and "bluff" are specific terms in poker.

Literally, in poker, to call a bluff means "To equal the bet of (the preceding bet or bettor) in a poker game" (American Heritage Dictionary).

Thus to CALL someone's bluff means to say, in effect, I think you're just bluffing; let's see what you've got; put your money where your mouth is; put up or shut up; etc.

By the way, Sax, when you post a question to this bulletin board, you do need to enter some sort of name in the "Name" box--either your real name or a made-up one--but you DON'T need to fill in the "E-Mail" box unless you want somebody to send you an e-mail.