What happens if you close both contacts at the same time? Glad you asked. From Wikipedia:
"Iambic keying or squeeze keying creates alternating dits and dahs. This makes sending some characters easier, like the letter C, by merely squeezing the two paddles together. In single-paddle, non-iambic keying, the hand motion would require alternating four times for C (dah-dit-dah-dit).
Iambic keyers function in one of at least two major modes: Mode A and Mode B."
See the wiki article for the differences in modes.
My newer ham radios have keyers built in.
Photos of my iambic paddles:
MFJ-564 similar to Bencher BY-1/2
Brown Bros Model BTL-A