Walking Turret

The Walking Turret was an Sentry Turret variant that was cut late in the development of Portal.

Overview
The Walking Turret was first revealed in the form of concept art during the PotatoFoolsDay ARG in 2011. Its design is similar to that of the standard Sentry Turret, only rounder, an orange colored eye, and a single side-mounted gun. In the concept art, it can be seen exiting a blue portal, implying that it may have been able to follow players throughout test chambers, and through their linked portals.

The Walking Turret could also collapse into a "fling pose", which presumably would allow it to fling itself through portals.

Valve animator Karen Prell explained that the Walking Turret was cut because it "didn't work best" as a game mechanic.