Walking up to the machine and bumping it will cost you one Penny, and roll the slots. You have no control over the results.
The symbols include Pills, bombs, hearts, keys, coins, flies, and technically dollar bills. Getting 3 Flies will result in either you getting a Pretty Fly or a black enemy fly being spawned in the room from the machine. Getting 3 Dollars (The symbol can't show up in other rolls, but the reels show it before the machine is destroyed) will make the machine self-destruct and produce a Dollar, a collectible that sets your money to 99 cents.
It is possible to find bombs (regular, troll, or 1+1 free), hearts (half heart, full heart, soul heart or eternal heart), keys (normal or golden), coins (penny, nickle, or dime), pills (any color), flies (Pretty Fly or black enemy fly), and dollar bill. Coins, Hearts and Bombs can all appear two at a time.
If the Slot Machine is caught in an explosion of any kind, it will be destroyed, dropping several items such as bombs, coins, keys, pills, hearts, or even gold chests.
Probabilities (from the source) Edit
The probabilities in the table are the default. If you have Lucky Foot, every outcome except for nothing or the machine exploding becomes 1.4 times more common. If you are Eve or have Mom's Pearl or Mitre, it is more likely that your hearts will be soul hearts, as usual.
|Event||Chance of occurring||Notes|
|two coins||5.19%||7/135||Each individual coin follows the usual distribution, as above.|
|1 + 1 Free||0.588%||147/25000|
|Pill||4.67%||7/150||The type of pill is randomly chosen from among the six occurring in the current game.|
|Machine explodes||2.00%||1/50||A few items drop. This shoves you away from the machine and causes damage if you are standing very close to it.|
|Pretty Fly||1.56%||7/450||Does nothing if you already have 3 orbitals (Pretty Fly, Halo of Flies, or Guardian Angel).|
|Dollar||0.467%||7/1500||An item which sets your money to 99¢. The machine explodes. Cannot be produced by the Portable Slot.|