When I worked for NTL, they got IBM in to support their internal servers (I looked after their internet facing servers and the intranet).
The intranet servers were in a rack one side of the datacenter, which IBM were responsible for so we had to move the servers over to our rack.
I was working with a young contractor called Kevin, and moving the servers (DL380 G1's) by balancing them on our heads (very health and safety concious).
I heard this loud crash and went running thinking Kevin had fallen and would be squashed under a server, and he did the same thinking the same about me.
So we stood there in the middle of the DC wondering if we were both OK, where did the crash come from, then we spotted the IBM engineer gingerly putting back one of their servers that he'd pulled out too far!
Talking of Kevin, the first time I took him to the DC I left him reading the information on the side of the backup tape silo (there was an A4 sheet giving the stats as to how many terabytes it could backup in an hour so something like that).
Then I heard this really girly scream so came running to find Kevin shaking with laughter.
He was looking through one of the inspection windows into the pitch black interior of the silo, when the robotic arm with it's two rows of red LEDs swung up at him

He said it was like a big red eyed monster coming at him!