Sticky Explody Ball is one of the Scientist's abilities. It is the third ability unlocked for the Scientist. The player usually spawns with two Sticky Explody Balls ready to use. It is thrown like a grenade, but sticks to whatever it lands on, whether it is a part of the environment or a plant, and even zombies. It deals 50 damage to every nearby plant when it explodes. It can be detonated after receiving certain amount of damage from the plants. It will detonate instantly when thrown on certain surfaces, such as the Golf Bomb. It takes 30 seconds to recharge one Sticky Explody Ball. Its alternate abilities are Mega Heal Bomb and Sticky Cheetah Ball (appears in Garden Warfare only). After a minute or so, it will explode on its own; this also applies to the Sticky Cheetah Ball.
The Sticky Explody Ball does exactly what you think it should. But did you know it only explodes in the presence of Plants? Neat!
A Sticky Explody Ball about to explode while on a Cactus
Shortly (around one second) after it is thrown, it cannot stick to anything and will bounce off instead.
It is possible to stick two of them on one plant. If this happens on a Sunflower, it is guaranteed to be vanquished unless it is a Metal Petal. Agent Peas, Hot Rod Chompers and Chomp Things (which the Chomper variants listed do not have their health upgrade) are also guaranteed to be vanquished with two of them on them.
It may be a reference to the stickybomb from Team Fortress 2.