Now that you know there's a possibility of finding...ah...unexpected protein sources in the romaine hearts, I'll share a tip.
I use this method of soaking leafy greens, broccoli, and other veggies with lots of impossible-to-get-to spots. I pick the veggies, bring them into the kitchen, and soak them once in water in the sink.
Let that water drain away. Now I add approx. 1 tsp. salt to the sink and soak again.
Warm water helps open the pores of the veggies so that the...unexpected protein creatures...can be exposed to the full effects of the salt. Swish the veggies around in the water a few times. Let the water drain away.
Rinse the salt (there isn't much, but for someone like me, there's still too much) off the veggies. They ought to be simply veggies by now.
Sunset Zone 17, USDA Zone 9