Parallax, in half

Hazard: The swing seats on the playsets can crack and break in half, causing the user to fall to the ground.

Incidents/Injuries: Escalade Sports has received 24 reports of the seats breaking, no injuries have been reported.

http://en.wikipedia.org/wiki/Parallax

Parallax

(păr'ə-lăks') 
n.
An apparent change in the direction of an object, caused by a change in observational position that provides a new line of sight.

[French parallaxe, from Greek parallaxis, from parallassein, to change : para-, among; see para-¹ + allassein, to exchange (from allos, other).]

parallactic par'al·lac'tic (-lăk'tĭk) adj.

[名][U][C]

1 視差：観察位置による対象物の変位.

2 《天文》視差.

3 《写真》（ファインダーとレンズの）視差.

［ギリシャ語parállaxis （para-そばに＋allássein変動する＋-sis（名詞語尾）＝そばに変動すること）］

in half

In two equal or roughly equal parts. For example, Let's cut this sheet in half. [Late 1500s]