When you have a big poop, and it lands sideways in the toilet, so it suspends the water like a bridge, spanning from one side of the bowl to the other. Upon flushing, the water will just sink beneath it, going down the pipe, and fill beneath the newly constructed "bridge". (The only way to flush a "suspension bridge" is to chop it up with a plunger).
"Man, I haven't taken a dump in 4 days. I totally just took one and made a giant suspension bridge."
A sexual endeavor that requires two couples to complete a "Bombs bursting in Air" and facing one another with the women making out (A Bombs Bursting in Air is where a female is in the reverse cowgirl position while the man is standing up holding her hands to support her with her legs around him to hold herself up). If done correctly, the men should be able to roll a matchbox car back and forth over the bridge.
"Oh man, my car totally crashed when Julie twisted while we were doing the suspension bridge"