Sam and Eric are twins. Though they are two individuals, they are identified as one with the nickname "Samneric".
Their companions can't tell them apart so instead of using their names, their friends combined their names and used it to address any one of the twins.
Samneric do things together. They think alike. Basically, they are identical in all ways from physical appearance to their characters.
Dorothy informs him of this in Chapter 4.
your not giving 20 points, you always give half