Selected experiments pertaining to SCP-731:
An attempt was made to drill into SCP-731-1 to recover samples and assess its durability. SCP-731-1 immediately transposed to the farthest available manhole in the containment network, preventing any damage. A repeat attempt while leaving no local manholes available for retreat is on hold pending the development of an easier way to track and recapture SCP-731-1 than was employed initially.
A tracking device was fastened to SCP-731-1 via a cable looped through the object's two pick holes. SCP-731-1 transposed to a new location within containment as soon as the technicians who had performed the task left the area. The cable was severed and both pieces remained at the original location. It is likely that any similar attempt to "tie down" SCP-731-1 through its pick holes would prove unsuccessful.
An ordinary domesticated cat was introduced to the street level of SCP-731 containment. When it eventually wandered onto SCP-731-1's surface it fell through in the same manner as a human subject, but no rat was disgorged from the underside. It appears that the cat was destroyed.
An ordinary domesticated cat, experienced in rat control, was introduced to the sub-street level of SCP-731 containment. The SCP-731-2 rats populating that level appeared terrified by the cat and fled in a normal manner, and the cat succeeded in catching and killing two of them. However, one hour and forty-five minutes into the experiment, the cat's feet were injured while pursuing a third. The cat was recovered and numerous metal slivers were found in its pads. It appears that the rats had gnawed these off of the interior of a degraded metal pipe and had deployed them as a field of primitive caltrops, with the fleeing rat luring the cat while itself navigating a predesignated safe path.
A ferret was introduced into the sub-street level of SCP-731 containment. The rats' anti-cat caltrop fields proved ineffective against this more agile foe, but it appears they were already prepared for this eventuality; the ferret succeeded in killing one rat and then was itself fatally wounded when it pursued a second into a confined tunnel. The rats had managed to find and sharpen a nail, rigging it to rise up from the ground at an angle when a platform immediately beyond it was stepped on to impale a pursuer.
Further predator introduction experiments have been suspended as it is not clear what more can be learned from this.
A pad of paper and a set of pencil graphites mounted on short plastic dowels suitable for gripping in a rat's jaws were introduced in the sub-street tunnel system of SCP-731 containment. While the presence of these items was immediately noticed by several of the rats, and 'word' apparently spread quickly through the system, it took over three hours for the rats to emerge from hiding and cautiously approach. Although they did not appear to be aware of the specific locations of the hidden surveillance cameras their behavior seemed to suggest that they were aware that they were being watched, apparently by deduction.
A heated squeaking 'argument' appeared to ensue among several of the rats, involving both conventional rodentine dominance/submission displays and recognizably humanlike forepaw gestures. Finally, one of the larger rats tore a sheet from the pad and used a graphite to write "FUCK YOU" in shaky but readable English. The rats then absconded with the graphites and the rest of the pad, succeeding in hiding them somewhere in the system not covered by surveillance.
It is recommended that the surveillance network be reviewed and these previously-unknown holes in its coverage filled.