We were in the middle of our production of Bye Bye Birdie tonight, and we had an occurrence that neither I nor our TD nor our tech professor can find an explanation for. Out of curiosity, I am asking here. I am sitting in my ASM post, and the grand is in in front of me and traveled open. It both flies and travels during the show, and we do not have a chance to attach the tension block to the floor. It had been open for probably around five minutes. Al of a sudden, I see, over the top of my music stand, the tension block steadily rising a good foot or so in maybe 1.5 seconds. I wait a minute and stare at it with the cast members who are standing next to me, then I walk over to it. Gently tugging on the hand line, it returns to its position. Any idea why this would happen? Is there really enough give in the cotton hand line for it to stretch that much? Would a stretched line restore itself that quickly and suddenly after sitting still for that long? Is there something else in the mechanics of a traveler that could cause the block to rise? I'm at a loss trying to explain it.