Guppy's Eye

Guppy's Eye is a passive item added in The Binding of Isaac: Repentance.

Effects[]

Displays the contents of Chests, Sacks, and Fire Places before they're opened/bombed.
This item belongs to the Guppy set. Collecting three items from this set will transform Isaac into Guppy.

Guppy's Eye does not show the contents of tinted rocks, Poops, and other obstacles.
Guppy's Eye does display enemies that can be contained within chests.
Chests and Sacks can only display up to four pickups at a time. If there are more than four, higher-value pickups like Bombs, Keys, and Soul Hearts will have priority on the display.
If a Red Chest looks like it doesn't have anything in it, it will teleport Isaac to the floor's Devil Room / Angel Room.
Due to how Trinkets generate, if a Chest displays a trinket, all future Chests will also display/give that trinket until it spawns in some way, at which point all Chests will display a new trinket.
Mimic Chests will change their contents whenever their spikes pop out. The only way to get the original drops is to open it with Flat File or Magneto.
This effect works on all non-ending chests, including Mom's Chest.
This item is substantially less useful in Greed Mode, due to the scarcity of chests.
The contents of Sacks or Chests that haven't spawned yet will still be revealed (for example, in rooms that spawn such Chests or Sacks when Isaac pressed a hidden switch, etc.).

This item was suggested on a Reddit post^[1] on the Binding of Isaac Subreddit.
Before it was added in The Binding of Isaac: Repentance, Guppy's Eye was an item in The Binding of Isaac: Four Souls, in which it forces all other players to play with their hands face-up on the table.
Its pickup text is possibly a reference to the description of the Rasmus mask from Hotline Miami.

PC L4WH 88YF ( Curse Room adjacent to spawn)

Bug!	If a Chest or Sack disappears due to Options? or the `G0NE S00N` seed, the preview of the Chest/Sack's contents will remain on screen where the chest was.