It can be raising its head or stiffen the body. Then you catch it again and repeat the process. Tree snakes are nice to photograph, since they can be placed on a branch on a level that is convinient for the photographer. Arrange light, adjust focus, etc. Have someone lift the jar, wait until the frog prepares itself for escape and take the picture in that split second before it jumps away.
Some frogs are very quick to jump.
I have some nice pictures of just bare ground or maybe a diffuse streak of a stretched out hind leg. Who wins and what to win This little quiz is not so very serious. And the prize book that I send to each winner is not a costly item. It is no longer held in stock by the publisher, who was kind enough to give me a rather high number of the unsold copies. I still get some revenue from the libraries that bought it, so at least I know that it is sometimes read.