Flounder wait in concealment on the bottom waiting for the tides to bring it a meal. With both eyes on one side and looking upward, its fixation on all things above it can lead to its demise and your benefit.
Most fish bite only when they are hungry with some occasionally displaying a territorial strike. Flounder however can be made to bite even with their bellies are full, it not for protection, then perhaps out of spite.
While studying flounder back in the late 1990s, I built a 1,000-gallon aquarium and kept a number of flounder in it.
Once after watching the fish feed voraciously on mullet, I decided to see how eager they would be bite, so I waited an hour and came back a rod and reel rigged with a curl-tailed grubbed tipped with shrimp, a lure flounder can rarely resist.
Dragging the bait a few inches of front of the flounder did nothing to draw their attention. However, when I put the lure over their eyes or near their mouth, the fish would strike very aggressively.
This was usually not the case in the tank. Before or during a feeding, the flounder would go after anything within six inches of them.
In the wild, this observation has paid big dividends during slack tides when flounder get lockjaw. Pattern casting in key flounder locales like the mouth of a small, marshy cut.
The key is to cover all of the water where you know flounder should be. By casting clockwise at 9, 12, 3 and then coming back and hitting 10, 1, 2 and repeating chances are you will make contact and make them mad enough to bite.
Most flounder anglers leave when the tides turn off or when they have not gotten a bite within a few minutes but if they exercise patience and practice pattern casting, slack tide can work for you.