None, a bassinet is an oblong basketlike bed for an infant; it's a basket with a hood over one end, for use as a baby's cradle.
If you are talking about the instrument that SpongeBob used at the Naughty Nautical Neighbors, it was actually a double bass (which he thinks is a bassinet).
The Double bass is the grandfather of the string family. At over 6 feet long, the double bass is the biggest member of the string family, with the longest strings, which allow it to play very low notes. And like the cello, the body of the double bass stands on the ground, supported by a metal peg, and the neck rests on your left shoulder.
It seems a lot of people are obsessed with anything relating to the word "fast", even when learning a musical instrument. Check out some tips on learning your instrument faster at About.com.