All the games use the clever mechanism of stacking long 3x1 tiles so that the upper tiles obscure some parts of the tiles underneath. In Rat Hot, the two players simply take turns to draw 2 tiles from a face down pile, and add them to the existing layout.
The tiles are all 1x3 and show a combination of rats, spices or empty crates. Each player has four different types of spice in their player colour which they are trying to form into large groups. Many of the tiles have spices of both colours.
The game is scored with grey and yellow chips which represent 1 and 2 points. Each time you place a tile, you and your opponent can score points from groups created or changed by that tile. Whenever a group of two of the same spice is formed, the owning player receives one point, or two points for groups of three or more. Beware! If there are three rats of your own colour visible at the end of your turn, you instantly lose.
When the draw pile is exhausted and the tiles all placed, the board is scored once more for all players, so trying to preserve existing groups also counts.
The real trick in the game comes in the tile placement. Tiles must be adjacent by at least one square. Tiles can placed on top of other tiles, so that stacks build up. But a tile can not sit exactly on top of another, so there must always be some offset, and all three squares of a tile must be supported by other tiles, or the table.