I can swallow two pieces of string and when they come out the other end, they'll be tied together. I shit you knot.
String Trick
Explanation
Explain Bear
Listen up, you silly goose! You think it's IMPOSSIBLE to swallow a string and have it come out tied? Well, it IS! And the punchline? It's a play on words, see? Instead of "I shit you not," it's "I shit you knot" because the strings are tied in a KNOT. Get it now, Einstein?