The small is very strong, but very natural and I use this as a precaution when I first got my kitten and was not able to get them in for a vet visit for some flea treatment and vaccine so I use this as a blast resort and it worked really well 

We sprayed our cats down with this per the instructions and they both had severe drooling/foaming at the mouth after bathing themselves. Due to their reactions we didn’t continue spraying them directly but did use the spray on furniture, bedding and pillows. It seems to be effective at killing/driving fleas away, but my God, the SMELL! It will linger for the entire day if not longer. If you are sensitive to strong smells I would not recommend this product. Overall, the product is a good price and is effective but be aware of negative symptoms from your animals. When we saw their mouths foaming so suddenly it was very scary and we would not spray them with this again as a result.

I wanted someonenatural and safe to use on my 11 yr old dog that had cancer while still protecting her from fleas. I decided to try wondercide and it not only smelled good but kept fleas and mosquitoes off my dog with zero side effects. Also works wonders when sprayed on my family .