You couldn't have known this, but your question has a connection with a real-life experience of mine, which is why I got the joke immediately:
I worked at a Sam Goody's record store in the '70s (the biggest one in the chain at the time, in Paramus, NJ) where we had one large main section for contemporary jazz and another smaller one for early jazz and Dixieland. A customer walked in one day and, not finding what he was looking for in the contemporary jazz section, pointed at the "B" section of the record bins and asked our manager, "Is Bix Beiderbeck here?," who heard the question as, "There's a big spider back here."
At which point my manager quickly stepped back a few feet and, standing on his tiptoes and craning his neck, VERY cautiously peered into the bin.
I was standing nearby and heard the customer's question the same way my manager did at first, but I knew some of Bix's music (I especially like his piano pieces, "In a Mist," etc.,) and quickly realized what he'd really said.
Later on, we all had a good laugh at our manager's expense -- his expression as he looked into the bins, imagining some eight-legged horror lurking there.