Playfulness and curiosity seem to indicate creative learning, many animals have it when young, the most adaptable and creative species have it as adults. Octopuses demonstrate it, solving puzzles even when there is no reward, they are solitary and don't learn from each other usually, although using scattered shells as armour against predators may be a learned behaviour. Dolphins play a lot, making bubble rings, and passing and dropping seaweed, and recent work suggests they can 'speak' images to each other using ultrasound. Sea otters, are very playful when young, and they bring up rock-anvils to crack sea urchins. Corvids and parrots show a great deal of playfulness, and great problem solving, though our insights on how much they can communicate are limited. Bees have been evidenced to exhibit playfulness, adding to cephalopods evudence it is a convergently evolved trait, in these very different branches of life long after they split.
The Mirror Test is thought to indicate self-awareness, although there are puzzles like pigs which by other measures are among the most intelligent mammals and show some tool use (sticks as 'spades' to dig out nests for litters), fail this test and it may reflect how they sense (smell as primary) or other factors than cognition.
Delayed gratification seems to provide evidence of impulse control. In humans it usually manifests around age three, and looking at the Dunbar Number we see evidence our neocortex evolved mainly to navigate socially problems, with wider problem solving a side-effect, and we can interpret this as it being for impulse control, with the neocortex only finishing it's structure age 25 or so in response to social pressures, and relating to emotional maturity from around that age. Delayed gratification has been studied in various animals.
Reciprical altruism relates to social intelligence, and supports social learning. As a social species we have cognitive biases towards valuing this which it important to correct for. Cooperative hunting, in wolves and orcas for instance, seems to be linked to advanced cognitive faculties. Human language, and especially written culture, seem to have given us a unique advantage, with each individual able to access the memesphere/noosphere/alayavijnana, which preserves innovations allowing the cumulative compounding of knowledge. Pointing seems a basic method of communication to us, but no other animals use it. The whites of human eyes help us follow where others are looking, and pointing may be an extension of gaze directing. Monkeys and apes that creche-rear young seem to share innovations more rapidly between same age individuals instead of between generations, for instance capuchins have as or more advanced tool use than chimpanzees, despite far smaller brains. Capuchins clearly have
a very strong concept of fairness. I think Haidt et al's Moral Foundations Theory could be giving insight into essential intuitions that facilitate social cooperation and learning.
Problem solving is probably the most widely accepted measure of intelligence, but it poses issues for fair comparison. Crows will quite quickly solve a problem requiring raising water level by adding stones from about 3 months old (equivalent relative to their lifespan to 1 year old human), but humans can't solve it until age 7 or so.
In summary, there are many measures of animal intelligence, and a great deal of dispute what they mean. I don't know what you mean by 'the presence of thought', there is very little we can do to explore that. Observation of active brains, specifically neural oxygen use, can be done with PET scans, but it requires being inside a big scanner currently, posing problems for observing normal cognitive functions. Otherwise, it's indicators, as above.
On the origins of emotions, you should read about embodied cognition, eg the SEP article on it. When we undergo a fight-or-flight response, blood is withdrawn from our intestines and digestion, and made ready for use by our muscles. This results in a 'gut feeling'. We can pick up non-conscious feelings of danger, and experience them through such a gut feeling. Similarly, our heart can react with preperations for expected circulatory demands, and we experience the hearts behaviour as the trigger for conscious emotional states. Feeling love is linked to dilated pupils (see ancient use of belladona for simulating this), which relates to a change in blood flow that facilitates arousal, and can be linked to the heart feeling like it is fluttering. The idea emotion happens only in the brain, is a very old-fashioned idea, thoroughly dismissed by extensive evidence. Our bodies feature evolved intelligent responses, like the fight-or-flight reaction, or blinking when things are near our eyes, which can involve no brain processing. The heart is just one locus of responses, the gut-brain axis is at least as significant, and increasingly related to mood disorders and stress responses.
Gaze-following is very important to human intelligence, and the game we have of pointing. We are extremely aware of when other humans look at us, so much so that there's a widespread superstition that we know someone is looking at us even when we can't see them (it's provably the result of confirmation bias). So it's not surprising we say 'eyes are the window into the soul'. We can have strong experiences that 'someone is looking back' when we make eye contact with an animal, and see it studying it and assessing us as we do it. But, it can also be misleading, for instance in many animals like apes and digs, direct eye contact is a claim for dominance, and will be experienced as a threat, compelling a less dominant animal to look down or away. We have a cognitive bias to overinterpret gaze, because with other humans we can get a lot of information from it, about mood and intentions, maybe even about curiosity and intelligence. Animals have different embodiments of their intelligence, and gaze can give valid clues, but can also mislead.
Can or should we be trying to flip the switch to make an animal
And I'm not totally sure what you mean. Perhaps you have in mind an experiment like in Rise of the Planet of the Apes, where an experiment makes a group of apes and their offspring dramatically more intelligent. This is highly unlikely. Intelligence is not simply about brain mass, but like a muscle involves response to use. And structurally, it has to be supporting solving specific problems that lead to reproductive benefits.
But, can we support animal species to become fully intelligent tool users like humans, what from science fiction especially David Brin's is called animal uplift, yes, and I would argue we have a moral duty at least not to prevent animals doing this, based on the reasoning of philosopher Peter Singer and his idea that the direction of moral progress is characterised by expanding the circle of our moral concerns. Just as we have moral duties to other species around preventing extinctions, we have duties to support them becoming what they can, and want, to be. We could enrich animal surroundings, and extend our interactions and study of animals like corvids and dolphins, in ways that support intelligent behaviours.
For more on embodied intelligence: Are levels of intelligence different levels of consciousness?
Moral progress: Why is it okay to eat meat but not to be cruel to animals?