The Soul Switcher, also known as the mind switcher or a mind transference device, is one of Ma'chello's inventions in which two individuals touching the device become trapped in the other individual's body. The process is irreversible. Only after another pair has been transferred is there a loop hole in which the device can allow groupings of individuals to be reintegrated into themselves.
Ma'chello designed the mind transfer device in the hopes of using it against Goa'uld infiltrators, depositing them in opposite bodies to mount their frustration and preoccupation into eventually defeating their original purpose. It is also possible he designed it for the very purpose which he eventually used it for -- switching into another body to evade capture by the Goa'uld. Initially using this to transfer himself into Dr. Daniel Jackson's body, Colonel Jack O'Neill and Teal'c were left frustrated when they fell victim to the machine themselves, requiring O'Neill to learn how to perform Kelno'reem and prevent Teal'c from shaving his head. After convincing Ma'chello to allow themselves to be switched back on the grounds that him stealing Daniel's body was no different from the Goa'uld stealing the bodies of others, Captain Samantha Carter was able to switch them back by realizing that they could use an alternate means of switching to place everyone's minds in the correct bodies. (SG1: "Holiday")