A creature can get skipped for a number of turns if it takes too long to execute. There is a limit to the time an animal can use for processing every turn which is calculated dynamically by the Terrarium each time it starts based on your computer's processing power.

To see how long your creature takes to process, you can open the Trace window, unselect "Show Organism Traces", and then select your creature. Note that this time will be different depending on the machine.

If you do break the limit Terrarium determines how many ticks worth of time you've gone over the limit and sets this property. You can examine this property to recover from conditions where your creature is skipped for a given number of turns. This is useful since you may not receive events that fire while during the time your creature's turn is being skipped.