The most recent edition of the Guide for the Care and Use of Laboratory Animals specifically mentions that floor space taken up by food bowls and other items, including toys and foraging devices may actually reduce the useable floor area within the enclosure (page 56). If the item takes up floor area and doesn’t allow use of the space below or above it, that area cannot be used to calculate space in the same way as perches in cat caging; if the animal can’t use the floor area below the perch, that floor area can’t be counted. There are some enrichment item designs that can actually provide additional usable surface area to replace that taken up by the footprint of the enrichment item. There are also lofts or perches which can be suspended from lids or wire bars that don’t impact the floor area, but rather provide additional useable surface. These designs allow the animals to make use of the space above and below the enrichment item and provide a more complex enclosure.