All 27 of the infants who moved off the centre board crawled out onto the shallow side at least once. Only 3 attempted to crawl onto the deep side.
Many of the infants crawled away from their mothers when they called to them from the deep side, others cried because they could not get to them without crossing the deep side. Infants patted the glass, yet the appearance of the drop prevented them from crawling across it.
Chicks, kids and lambs: never stepped onto the deep side, even at one day old. If a kid or lamb was placed on the glass it froze in a posture of defence.
Rats: hooded rats explored either side as long as they felt the glass with their whiskers. When the centre board was higher, they nearly always went to…